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VESUVIUS 
Eruption  ol  A|>iil,  u/jO.     I'.iiiibsion  of  gas,  ashes,  and  sand  as  seen  from  the  Observatory. 


)0 


MAURY-SIMONDS  PHYSICAL   GEOGKArHi 


PHYSICAL    GEOGRAPHY 


BY 
M.    F.    MAURY.    LL.D. 

LATE    SUPERINTENDENT   OF   THE   NA\'Al.   OBSERVATORY,    WASHINGTON,    D.C. 

REVISED    AND    LARGELY    REWRITTEN 
BY 

FREDERIC    WILLIAM    SIMOXDS,   Ph.D. 

PROFESSOR   OF  GEOLOLiV    IN    THE    UNIVERSITY   OF  TEXAS 


/7577 


NEW  YORK  •:•  CINCINNATI   •:•  CHICAGO 

AMERICAN    BOOK    COMPANY 


■tiy 


1908 


Copyright,  1908,  by 
FREDERIC  WILLIAM  SIMONDS. 

Entered  at  Stationers'  Hall,  London, 
maury-simonds  phys.  geog. 


\44 


PREFACE 

The  advance  of  geographic  science  has  been  so  great  during 
the  last  decade  that  a  thorough  revision  of  the  older  text-books 
has  become  imperative.  To  the  end  that  Maury's  Physical 
Geography  may  maintain  its  position,  it  has  been  the  writer's 
privilege  not  only  to  revise,  but  largely  to  rewrite  that  well- 
known  book.  In  so  doing  an  attempt  has  been  made  to  pre- 
serve as  far  as  possible  the  plan  of  the  older  work  —  a  plan 
that  has  met  the  approval  of  a  generation  of  teachers  —  and, 
at  the  same  time,  to  modernize  the  text  thoroughly. 

In  the  matter  of  illustrations,  the  present  volume  will  be 
found  exceedingly  attractive  and  the  adoption  of  a  smaller  page 
will  add  much  to  the  reader's  comfort. 

In  the  preparation  of  this  edition,  acknowledgments  are 
due  to  many  persons,  especially  to  Dr.  William  J.  Battle  and 
Dr.  William  T.  Mather  of  the  University  of  Texas  —  the 
former,  for  the  use  of  some  of  his  excellent  photographs  of 
Egyptian  scenery ;  the  latter,  for  timely  suggestions  which 
have  added  materially  to  the  accuracy  of  the  text.  Acknowl- 
edgments are  also  made  to  Mr.  Sterling  R.  Fulmore  for  Ha- 
waiian, Australian,  and  New  Zealand  views ;  to  Professor  A.  J. 
Henry,  of  Washington,  B.C.,  for  cloud  views  ;  to  Mr.  W.  E. 
Seright,  of  Stafford,  Kansas,  for  the  unique  photograph  of  a 
tornado ;  to  President  D.  S.  Jordan,  of  Leland  Stanford  Junior 
University,  for  California  earthquake  views ;  and  to  Professor 

S 


6  PREFACE 

H.  L.  Fairchild,  of  the  University  of  Rochester,  for  photo- 
graphs of  drumlins,  kames,  and  eskers.  The  diagrams  and 
most  of  the  maps  have  been  drawn  by  the  writer  or,  under 
his  direction,  by  Mr.  N.  P.  Pope. 

FREDERIC   W.    SIMONDS. 

The  University  of  Texas,  Austin. 


CONTENTS 


Introductory 


PART    I.  — THE    EARTH 

CHAPTER 

I.  The  Earth  and  the  Solar  System  . 

II.  The  Shape,  Size,  and  Density  of  the  Earth 

III.  The  Motions  of  the  Earth 

IV.  Terrestrial  .Magnetism 
V.  Internal  Heat  of  the  Earth 

VI.     Volcanoes     .... 
VII.     Earthquakes 


II 

i8 

23 
32 
40 
46 
60 


PART    II.— THE    LAND 

VIII.     The  Land  Masses 70 

IX.     Relief  of  the  Land 75 

X.     Relief  Forms  of  North  a.nd  South  America         .        .  95 

XI.     Relief  Forms  of  Europe.  .Asia.  Afrk  a.  and  .Australia  114 

XII.     Islands 128 


PART    III.— THE   WATER 


XIII.  Properties  of  Water 

XIV.  Waters  of  the  Land  . 
XV.  Drainage       .... 

XVI.  The  Sea  and  the  Oceans  . 

X\'II.  Wa\es.  Tides,  and  Currents 


136 
140 
165 

179 


CONTENTS 


PART    IV.  — THE    ATMOSPHERE 

CHAPTER 

XVllI.  Physical  Properties  of  the  Atmosphere 

XIX.  Climate      .... 

XX.  Atmospheric  Circulation 

XXI.  Storms        .... 

XXII.  Moisture  of  the  Air 

XXIII.  Rain 

XXIV.  Hail,  Snow,  and  Glaciers 
XXV.  Electrical  and  Optical  Phenomena 


PAGE 

200 
2IO 
2l8 
229 

239 
249 
258 
27s 


PART    v.  — LIFE 

XXVI.     Animals  and  Plants         .......  280 

XXVII.     The  Distribution  of  Useful  Plants      ....  288 

XXVIII.     The  Distribution  of  Animals 292 

XXIX.     Man 311 

XXX.    Geographical  Distribution  of  Labor   ....  322 


APPENDIX 
XXXI.    Physical  Geography  as  a  Science 


328 


INTRODUCTORY 

Physical  Geography  deals  with  the  world  in  the  present  stage 
of  its  existence.  It  considers  the  machinery  which  makes  day 
and  night,  seedtime  and  harvest ;  which  lifts  the  vapor  from 
the  sea,  forms  clouds,  and  waters  the  earth ;  which  clothes  the 
land  with  verdure  and  cheers  it  with  warmth,  or  covers  it  with 
snow  and  ice.  Physical  Geography,  moreover,  treats  of  the 
agents  that  cause  the  wonderful  circulation  of  waters  in  the 
sea;  that  diversify  the  continents  with  mountains,  hills,  plains, 
and  valleys,  and  embellish  the  landscape  with  rivers  and  lakes. 
It  views  the  earth  —  its  surface,  its  waters,  and  its  enveloping 
atmosphere  —  as  the  scene  of  operation  of  great  physical  forces, 
which  by  their  united  action  render  possible  the  life  of  plants 
and  animals ;  and  studies  the  life  of  the  globe,  both  terrestrial 
and  aquatic,  noting  particularly  the  circumstances  which  are 
favorable  or  adverse  to  its  development. 

It  has  been  found  convenient  to  present  the  topics  treated  in 
the  following  order  :  — 

I.    The" Earth. 
II.    The  Land. 

III.  The  Water. 

IV.  The  Atmosphere. 
V.    Life. 


_Of_NEPTytvlE_ 

The  Solar  System 


PART    I.  — THE    EARTH 


I.  THE  EARTH  AND  THE  SOLAR  SYSTEM 

/7377 

The  Solar  System.  —  By  the  ancients  the  earth  was  regarded 
as  the  center  of  the  universe.  Men  saw  the  sun  in  the  same 
part  of  the  heavens  morning  after  morning,  and  when  his  light 
faded  at  night  they  saw  the  stars  in  nearly  the  same  positions 
as  on  the  preceding  night.  •  Hence  they  concluded  that  the 
sun  and  stars  all  move  around  the  earth  once  in  24  hours. 
Careful  observation  seemed  to  confirm  this  idea.  Astronomers 
watched  the  heavens;  they  mapped  the  stars;  they  recorded, 
from  night  to  night,  the  places  of  the  brightest  among  them. 
As  a  result,  they  found  that  the  position  of  some  remains 
unchanged  with  reference  to  that  of  their  companions,  while 
the  position  of  others  varies  perceptibly. 

The  former  were  called  fixed  stars ;  the  latter  received  the 
name  planets,  from  a  Greek  \yord  meaning  zvanderers.  For 
several  centuries,  ho.wever,  astronomers  have  known  that  the 
ancient  idea  was  a  mistake.  The  sun,  not  the  earth,  is  the 
center  around  which  the  planets  revolve,  and  the  earth  itself 
is  a  planet.  The  planets  are  not  self-luminous,  but  shine  by 
reflected  sunlight.  Their  paths  of  motion,  or  orbits,  are  nearly 
circular,  and  they  all  journey  around  the  sun  in  nearly  the  same 
plane.  In  their  regular  order,  beginning  with  that  nearest  to 
the  sun,  the  planets  are  Mercury,  Venus,  Earth,  Mars,  Jupiter, 
Saturn,  Uranus,  and  Neptune. 

With  the  exception  of  Mercury  and  Venus,  they  are  attended 
by  one  or  more  moons,  or  satellites.  The  sun,  planets,  and 
satellites,   together  with   a   number  of   small   planetary  bodies 


12  THE   EARTH   AND   THE   SOLAR   SYSTEM 

called  asteroids,  or  pla7ietoids,  which  revolve  in  paths  between 
Mars  and  Jupiter,  constitute  the  Solar  System,  so  named  from 
the  Latin  sol,  the  sun. 

Within  the  limits  of  the  Solar  System  there  are  also  comets  and  meteoric 
swarms.  The  former  are  celestial  bodies  usually  consisting  of  a  head,  with  a 
very  bright  spot  which  gradually  shades  into  a  less  luminous  portion,  or  coma, 
and  a  tail,  or  streamer. 


GiAcoBiNi's  Comet,  December  29,  1905 

From  photograph  by  Professor  E.  E.  Barnard,  Yerkes  Observatory. 

Owing  to  the  movement  of  the  camera,  which  was  kept  focused  on  the  comet  during  the 
exposure,  the  stars  appear  as  lines  instead  of  points. 

Comets  seem  to  be  composed  of  matter  in  a  highly  rarefied  state,  for  even 
sinall  stars  are  visible  through  them.  Some,  from  their  movements  around 
the  sun,  must  be  considered  members  of  the  Solar  System ;  others  appear  as 
casual  visitors,  passing  never  to  return. 


The  Henderson,  North  Carolina,  Meteorite 

Two  views.     From  proceedings  of  the  U.  S.  Nat.  Mus.,  Vol.  32. 

13 


H 


THE   EARTH   AND   THE   SOLAR   SYSTEM 


The  meteoric  swarms  seem,  in  some  instances,  to  follow  the  orbits  of  cer- 
tain comets ;  in  others,  the  number  of  meteors  is  so  great  as  apparently  to  fill 
the  entire  circuit  of  their  own  orbits.  In  either  case,  when  they  encounter 
the  atmosphere  of  the  earth,  there  is  a  brilliant  clisjDlay  of  shooting  stars,  the 
so-called  meteoric  showers. 

The  Sun.  — The  sun  is  also  a  star.  From  it  the  planets  derive 
both  heat  and  light.  This  vast  ball,  or  sphere,  is  more  than  a 
million  times  as  large  as  the  earth.     Were  the  earth  placed 

at    the   sun's    center, 
^  ~~~~^  the  latter  body  would 

reach  so  far  into  space 
as  to  extend  nearly 
200,000  miles  beyond 
the  orbit  of  the  moon, 
or  almost  440,000 
miles  beyond  the 
earth's  surface. 

The  sun  is  in  an 
intensely  heated  con- 
dition, and  clouds  of 
incandescent  gases 
project  outward  from 
its  surface  for  thou- 
sands of  miles  into 
space.  From  examina- 
tions made  with  the 
spectroscope  it  is 
known  to  contain  many  substances  entering  into  the  composition 
of  the  earth. 

Origin  of  the  Solar  System. — The  sun  and  the  planets  are 
composed  of  the  same  kinds  of  matter  and  have  similar  forms 
and  motions.  Many  astronomers  and  philosophers  have  tried 
to  combine  these  facts  and  others  into  an  explanation  of  the 
origin  of  the  Solar  System.  Such  explanations  are  termed 
hypotheses.  Of  these  hypotheses  at  least  two  merit  attention  ; 
namely,  the  lubiilar  ■a\\<\  \\\<i platietesiinal. 


Diagram  showing  the  Comparative  Sizes  of 
THE  Earth,  the  Orbit  of  the  Moon,  and 
THE  Sun's  Disk 


iiii:  NFnri.AR  hypothesis 


15 


DlAiiKAMMATlC    1  LI  I  S 1  KATIU.N    UK   THE    .\EliULAK    lIVl'OTHEslb 

Showing  ihe  abandoned  rings  in  various  stages.  ^.S'  is  the  central  sun  ;  a,  b,  c,  successive 
rings;  d,  e,f,g,  denser  portions  of  certain  rings  which,  in  the  process  of  planet  forma- 
tion, are  drawing  the  less  dense  portions  within  themselves. 

The  Nebular  Hypothesis. — This  hypothesis,  which  apparently 
fails  to  meet  sonie  of  the  necessary  physical  tests,  assumes  a  vast 
glowin,^  cloud,  or  nebula,  of  o:aseous  matter  extending  beyond 


S.\TURN    AND   HIS    RINGS 


the  orbit  of  the  farthest  planet  and  endowed  with  a  slow  rotary 
motion.     As    this   nebula    cooled    and    contracted,   its    rotation 


i6 


THE    EARTH    AND   THE   SOLAR   SYSTEM 


became  more  rapid  and  it  became  disklike  in  form.  As  the 
contraction  continued,  partial  or  complete  rings  similar  to  the 
rings  of  Saturn  were  separated  from  the  outer  edge.  These, 
contracting  toward  their  densest  parts,  became  planets,  revolv- 
ing around  the  central  nucleus,  which  we  call  the  sun. 

The  Planetesimal  Hypothesis.  —  This  hypothesis  assumes  the 
sun  as  the  origin  of  the  planets.  Attracted  by  an  approaching 
star,  a  sun  wave  of  gaseous  matter  flew  off  forming,  with  the 


ASTEROIDS  MS 


Relative  Sizes  of  the  Sun  and  Planets 

The  names  of  the  planets  are  indicated  by  their  initial  letters  except  Mercury  and  Mars 

which  are  indicated  by  My  and  Ms  respectively. 


central  nucleus,  a  spiral  nebula.  This  cooled  and  condensed  into 
small  separate  particles  (planetesimals)  like  the  meteoric  dust 
that  sometimes  falls  upon  the  earth.     Some  of  these  particles, 


THE    EARTH   AND  THE   UNIVERSE  1 7 

colliding  and  uniting,  formed  small  bodies,  which  were  enlarged 
by  continual  showers  of  planetesimals  and  thus  became  planets. 

The  Relative  Sizes  of  the  Sun  and  Planets.  —  The  relative 
sizes  of  the  sun  and  planets  are  shown  in  the  cut  on  page  i6,  in 
which  the  diameter  of  the  sun  has  been  reduced  to  3.]  inches. 
It  has  been  calculated  that  the  sun  contains  600  times  the 
united  volumes  of  all  the  bodies  revolving  about  it.  Even  the 
larger  planets  are  greatly  inferior  to  it  in  size,  while  the  smaller 
planets  are  comparatively  insignificant. 

If  the  earth  be  represented  by  a  globe  one  foot  in  diameter, 
the  sun  must  be  represented  by  a  sphere  35  yards  in  diameter, 
placed  2\  miles  from  the  globe,  in  order  to  show  in  proper  pro- 
portion the  size  of  the  two  bodies  and  the  distance  between 
them.  In  a  similar  manner  Jupiter,  the  largest  planet,  would 
be  represented  by  a  globe  3|  yards  in  diameter  at  the  distance 
of  1 1  miles  from  the  sun. 

The  Earth  and  the  Universe.  —  From  the  astronomer  we  learn 
that  most  of  the  fixed  stars  are  possibly  the  suns  of  other  systems 
resembling  our  own,  but  in  many  cases  vastly  larger.  From 
him  we  also  learn  that  the  heavens  are  filled  with  unknown 
numbers  of  such  systems.  Hence  follows  the  conclusion  not 
only  that  the  earth  is  one  of  the  smaller  members  of  the  solar 
system  but  that  the  solar  system  is  itself  one  of  the  numerous 
systems  that  fill  the  immensity  of  space.  With  this  in  mind  it 
is  possible  to  realize  that  i/ie  eartJi  is  an  exceedingly  small  part 
of  tJie  created  nniverse. 

The  subordinate  position  of  the  Solar  System  is  strongly  suggested  by  the 
face  that,  under  the  influence  of  the  other  suns  of  the  universe,  it  appears  to 
be  moving  through  space  in  the  direction  of  the  constellation  Hercules. 


M.-S.  PHVS.  GEOG.  —  2 


II.     THE    SHAPE,    SIZE,    AND    DENSITY    OF   THE 

EARTH 

Shape  of  the  Earth. — As  inhabitants  of  the  earth  we  are 
greatly  impressed  with  its  surface  irregularities.  What  a  con- 
trast between  lofty  summits  of  the  Andes  or  Himalaya  mountains 


Diagram  illustrating  the  Curvature  of  the  Earth 

and  the  depths  of  the  ocean  basins!     Can  a  body  exhibiting 
so   many  and   so   great  inequalities  fall  within   the  boundary 


Diagram  illustrating  the  Curvature  of  the  Earth  by  the  Increased 
Range  of  Vision  in  ascending  a  Height 


of  a  regular  geometric  form  ?     We  are  merely  suffering  from 
the  nearness  of  the  view.     Could  we  station  ourselves  on  the 


SHAPE  OF  THE   EARTH 


19 


moon,  then  as  we  beheld  the  earth,  its  surface  irregularities 
would  no  longer  confuse  us.  In  comparison  with  the  whole 
they  would  sink  into  insignificance,  and  the  earth  would  appear 
as  a  great  rounded  globe  or  sphere  not  varying  in  its  general 
shape  from  the  other  planets. 

There  is  ample  proof  that  the  surface  of  the  earth  is  curved. 

I.  Watch  ships  as  they  sail  seaward.  Do  they  not  pass  over  a  curved 
surface  as  their  hulls,  then  their  sails,  and  lastly  their  topmasts,  disappear  from 
view  ? 


An  Eclipse  of  the  Moon 

From  photograph  by  G.  W.  Ritchey,  Yerkes  Observatory. 

Partial  phase  of  the  total  eclipse  of  October  16,  1902,  10: 33  P.M.      The  margin  of 

the  earth's  shadow  is  curved. 


2.  Stand  at  the  foot  of  a  hill  overlooking  a  plain  and  note  the  boundary 
line  or  limit  of  vision.  Now  climb  to  the  summit  and  note  the  increased 
range  of  vision.     Were  the  earth  flat,  this  would  not  occur. 

3.  Observe  the  curved  margin  of  the  earth's  shadow  during  an  eclipse  of 
the  moon. 

The  sun,  earth,  and  moon  being  now  in  the  same  straight  line,  the  shadow 
of  the  earth  extends  in  the  form  of  an  elongated  cone  far  beyond  the  orbit  of 
the  moon.     That  body,  in  the  course  of  its  movement,  cuts  this  shadow  which 


20 


THE   SHAPE,    SIZE,   AxMD   DENSITY   OF  THE   EARTH 


obscures  its  face.     While  the  margin  of  the  shadow  is  ill  defined,  it  is,  never- 
theless, sufficient  to  show  the  general  curvature  of  the  surface. 
That  the  earth  is  of  a  spherical  shape  is  also  shown  — 

1.  By  voyages  and  journeys  "  round  the  world."' 

2.  By  the  measurement  of  arcs  of  great  circles. 

3.  By  the  fact  that  the  horizon  when  viewed  from  a  high  point  rising  above 
a  level  plain,  as  from  a  tower  or  the  summit  of  a  hill,  is  always  circular,  a 
property  belonging  only  to  spherical  bodies. 

The  Earth  an  Oblate  Spheroid.  —  The  particles  of  a  rotating 
body  tend  to  fly  off  in  straight  lines.     This  tendency  is  called 

centrifugal  force. 
Gravitation  tends  to 
make  a  mass  spher- 
ical. These  two 
forces  combined 
have  caused  the 
earth,  which  is  some- 
what plastic  and 
elastic,  to  assume  a 
slightly  flattened 
spherical  form  called 
an  oblate  spheroid. 
Its  longest  diameter 
is  nearly  7927  miles 
and  its  shortest  di- 
ameter nearly  7900 
miles.  Its  greatest 
circumference  is 
about  24,900  miles, 
its  smallest  circum- 
ference about  24,860 
miles,  and  the  area  of 
its  surface  197  mil- 
lions of  square  miles. 


Diagram  for  demonstrating  the  Spheroidal 
Form  of  the  Earth 

The  horizon  when  viewed  from  a  high  point,  A,  B,  or  C, 
is  a  circle 


The  oblateness  of  the  earth  is  shown  by  the  fact  that  although  the  weight 
of  a  body  on  its  surface  is  nearly  constant,  it  is  slightly  greater  in  high 
latitudes. 


DENSITY   OF    THE    EARTH 


21 


Density  of  the 
Earth.  —  The  exterior 
is  the  only  part  of  the 
earth  concerning 
which  we  have  definite 
knowledge.  Here  we 
encounter  matter  in 
its  three  forms :  the 
gaseous,  represented 
by  the  atmosphere ; 
the  liquid,  represented 
by  the  hydrosphere, 
or  water  areas ;  and 
the  solid,  represented 
by  the  lithosphere, 
or  "crust."  These 
spheres  are  arranged 
in  the  order  of  their 
densities,  and  although 
the  air  and  water  are 
often  spoken  of  as  the 
earth's  coverings,  they 
are  as  much  of  the 
planet  as  the  litho- 
sphere. 

On  account  of  pres- 
sure each  of  these 
spheres  should  become 
denser  in  the  direction 
toward  the  center  of 
the  earth.  The  bot- 
tom of  the  atmosphere, 
especially  that  part 
resting  on  the  sea,  is 
densest,  as  it  is  com- 
pressed by  the  weight 


JUPITER 


SATURN 


NEPTUNE 


URANUS 


^   EARTH 
@    VENUS 
The  Planets  arranged  according  to  Size 


®   MARS 
Q   MERCURY 


22 


THE   SHAPE,   SIZE,   AND   DENSITY   OF  THE   EARTH 


of  the  air  above  it.  Similarly,  the  water  in  the  deepest  parts 
of  the  sea  should  be  densest,  but  water  is  practically  a  non- 
compressible  medium.  It  does  not  seem  unreasonable  that  the 
materials  constituting  the  Hthosphere  should  increase  in  density 


Section  of  the  Earth 
A,  atmosphere ;  B,  hydrosphere ;  C,  lithosphere ;   N,  nucleus. 

toward  the  earth's  nucleus  or  centrosphere,  which  must  be  the 
densest  part  of  all.  That  such  is  the  fact  appears  to  be  proved 
by  numerous  experiments  which  go  to  show  that  while  the 
density  of  the  outer  portion  of  the  lithosphere  is  about  2.5, 
that  of  the  lithosphere  and  nucleus  together  is  not  far  from  5.5. 


III.     THE    MOTIONS   OF   THE   EARTH 

Effects  of  the  Earth's  Motions.  —  The  earth  has  two  motions 
which  greatly  influence  all  things  living  upon  it,  whether  animals 
or  plants.  The  first  is  a  daily  motion,  or  rotation  on  its  axis, 
by  which  there  is  produced  an  alternation  of  light  and  darkness 
called  day  and  night.  The  second  is  a  yearly  motion,  or  revolu- 
tion about  the  sun,  by  which  seasonal  changes  are  produced  and 
the  many  consequences  flowing  from  them. 

Meridians.  —  When  the  sun  reaches  its  highest  point  for  the 
day,  the  shadow  cast  by  a  plumb  line  extends  north  and  south. 
Hence  north-and-south  lines  are  called  meridians,  or  midday 
lines.  All  meridians  when  produced  meet  at  the  ends  of  the 
earth's  axis,  called  the  poles.  The  meridian  of  any  place  can 
be  determined  roughly  by  means  of  a  vertical  rod  on  a  level 
table.  Beginning  about  half  an  hour  before  midday,  mark 
at  intervals  of  two  minutes  the  end  of  the  shadow  cast  by  the 
rod  till  the  shadow  lengthens.  The  line  from  the  end  of  the 
shortest  shadow  to  the  base  of  the  rod  points  north  and  south 
and  lies  in  the  meridian  of  the  place. 

Parallels.  —  Lines  at  right  angles  to  any  meridian  extend 
east  and  west.  Since  they  are  parallel  circles  around  the  earth, 
they  are  called  parallels.  The  parallel  midway  between  the 
poles  is  called  the  equator,  since  it  divides  the  earth  into  two 
equal  parts,  or  hemispheres. 

Position.  —  The  position  of  a  place  is  determined  when  we 
know  its  distance  north  or  south  of  the  equator  and  its  distance 
east  or  west  of  a  standard  meridian. 

Latitude  and  Longitude. —  The  distance  north  or  south  from 
the  equator,  measured  in  degrees  along  a  meridian,  is  called 
latitude.     The    latitude  of  the  equator  is  o°,  and  of  the  poles 

23 


24 


THE   MOTIONS   OF  THE   EARTH 


90°,  the  highest  latitude.  Distance  east  or  west  from  a  stand- 
ard meridian  measured  in  degrees  along  a  parallel  is  called 
lojigitude.  The  meridian  of  Greenwich,  near  London,  is  com- 
monly taken  as  the  standard.  The  longitude  of  the  Greenwich 
meridian  is  0°,  and  the  longitude  of  the  most  distant  meridian  is 
180°.  The  sun  crosses  all  meridians,  that  is,  360°  of  longitude, 
every  24  hours,  at  the  rate  of  1 5°  an  hour.     Hence  the  difference 

in  longitude  between  two  places  is 
equal  to  15°  multiplied  by  the  dif- 
ference in  time  in  hours.  The  differ- 
ence in  time  can  be  determined  by 
means  of  accurate  timekeepers  com- 
monly called  chronometers,  and  by 
telegraph.  The  length  of  a  degree 
of  longitude  is  about  68.7  miles  at 
the  equator  and  decreases  gradually 
to  o  at  the  poles. 

Measuring  Latitude. —  The  line  of 
the  earth's  axis  passes  close  to  a  star 
in  the  northern  heavens  called  the 
North  Star  or  the  polestar.  To  an 
observer  at  the  equator,  the  polestar 
seems  to  be  at  the  horizon.  As  he 
travels  northward  it  seems  to  rise  in 
DiAGRAM~sHowrN7THE  Posi-  ^hc  heavcus  a  degree  for  every 
TioN  OF  THE  NoRTH  STAR    dcgrcc  of  latltudc  till  at  the  pole, 

IN  THE   HEAVENS  ^^o  ^_^   -^  j^  -^^  ^j^^  ^^^^-^j^^  ^^  ^^o  ^^^^^ 

the  horizon.  In  other  words,  the  latitude  of  a  place  north  of 
the  equator  may  be  found  by  measuring  the  altitude  of  the 
polestar. 

At  the  equinoxes  (see  p.  26)  the  sun  is  directly  over  the 
equator,  and  on  these  dates  the  latitude  of  a  place  is  equal 
to  the  angular  distance  from  the  zenith  to  the  midday  sun. 

The  Problem  of  Eratosthenes.  —  In  240  b.c.  Eratosthenes,  a 
famous  Greek  astronomer,  measured  an  arc  of  a  meridian  by 
means  of  the  noon  shadow.      He  found  that  the  angular  differ- 


NORTH 
STAR  f- 

* 

/^                   i 

NORTH 
POLE 

i     '     ■''^'Ti|| 

SOUTH 
POLE 

VARIATION'S   IN   THE    LENGTHS   OF   DAY   AND   NIGHT  27 

B  in  its  orbit.  The  direction  and  inclination  of  its  axis  remain- 
ing the  same,  it  will  be  seen  that  the  direct  rays  of  the  sun  have 
apparently  moved  north  and  that  they  now  fall  upon  the  Tropic 
of  Cancer.  Moreover,  as  the  sun  always  illumines  one  half  of 
the  earth,  the  entire  region  within  the  arctic  circle  is  in  daylight, 
while  the  corresponding  region  within  the  antarctic  circle  is  in 
darkness ;  that  is,  during  the  passage  of  the  earth  from  A  to  B 
the  great  circle  of  illumination  has  changed  its  position  so  that 
instead  of  passing  through  the  poles  it  now  passes  through  two 
alternate  points  23|°  from  the  poles. 

As  the  great  circle  of  illumination  passes  beyond  the  north 
pole,  the  days  in  the  northern  hemisphere  constantly  increase  in 
length,  until  at  B,  the  summer  solstice,  or  June  22,  there  is  ex- 
perienced the  longest  day  and  the  shortest  night  of  the  year. 
On  the  other  hand,  in  the  southern  hemisphere  the  opposite 
conditions  prevail.  During  the  passage  of  the  earth  from  A  to 
B  the  days  grow  constantly  shorter,  and  the  nights  longer ;  thus 
in  the  two  hemispheres  there  is  an  alternation  in  the  lengths  of 
the  periods  of  light  and  darkness. 

At  C  the  sun's  rays  fall  again  directly  upon  the  equator,  the 
great  circle  of  illumination  passes  through  the  poles,  and  the 
days  and  nights  are  equaj.  This  is  the  autumnal  tquinox,  or 
September  22. 

At  D  the  direct  sun  rays  fall  upon  the  Tropic  of  Capricorn, 
and  the  great  circle  of  illumination  reaches  only  the  arctic  circle, 
but  in  the  southern  hemisphere  sunlight  extends  beyond  the 
pole  to  the  antarctic  circle.  It  will  be  seen  that  the  conditions 
which  prevailed  when  the  earth  was  at  B  are  completely  re- 
versed. Then  the  northern  hemisphere  experienced  its  longest 
day  and  its  shortest  night,  now  the  southern  hemisphere  has 
its  longest  period  of  light  and  its  shortest  period  of  darkness. 
This  is  the  ivinter  solstice,  or  December  22. 

The  length  of  days  and  nights  varies  with  the  latitude.  At  the  equator,  or 
0°,  they  are  always  equal;  that  is,  twelve  hours  long.  At  latitude  30.8°  the 
longest  day  is  14  hours  ;  at  latitude  58.5°,  18  hours  ;  at  latitude  63.4°,  20  hours  ; 
at  latitude  66.5^.  24  hours.     Within  the  arctic  or  antarctic  circles  the  longest 


28  THE   MOTIONS   OF  THE   EARTH 

day  or  greatest  period  of  sunlight  exceeds  24  hours,  being  in  latitude  67.4°,  I 
month  ;  in  latitude  73.7°,  3  months  ;  in  latitude  90^,  6  months. 

The  arctic  day  and  the  arctic  night  have  been  thus  described  by  an  eye- 
witness :  — 

"  The  sun  moves  quickly  in  these  latitudes  from  the  first  day  he  peers  over 
the  horizon  in  the  south  until  he  circles  round  the  heavens  all  day  and  all 
night ;  but  still  quicker  do  his  movements  seem  when  he  is  on  the  downward 
path  in  autumn.  Before  you  know  where  you  are  he  has  disappeared  and  the 
crushing  darkness  of  the  arctic  night  surrounds  you  once  more. 

"On  September  12  we  should  have  seen  the  midnight  sun  for  the  last  time 
if  it  had  been  clear  and  no  later  than  October  8  we  caught  the  last  glimpse 
of  the  sun's  rim  at  midday.  Then  we  plunged  into  the  longest  Arctic  night 
any  human  beings  have  ever  lived  through  in  about  85  north  latitude.  Hence- 
forth there  was  nothing  that  could  be  called  daylight,  and  by  October  26 
there  was  scarcely  any  perceptible  difference  between  day  and  night."  —  Report 
of  Captain  Otto  Sverdrup,  Appendix  to  Nansen''s  Farthest  North. 

Sidereal  and  Solar  Days.  —  It  is  the  rotation  of  the  earth  on 
its  axis  that  gives  rise  to  the  time  divisions  in  common  use. 
The  time  of  a  rotation  of  the  earth  can  be  measured  accurately 
by  means  of  the  stars,  and  is  called  a  sidereal  day,  from  the  Latin 
sidiis,  a  star.  It  is  the  time  unit  used  by  astronomers.  The 
time  between  two  successive  noons  is  called  an  apparent  solar 
day.  As  the  earth  rotates  it  moves  onward  in  its  path  around 
the  sun,  faster  as  it  approaches  the  sun,  and  slower  as  it  recedes. 
Hence  apparent  solar  days  are  somewhat  longer  than  sidereal 
days,  and  vary  slightly  in  length.  The  average  length  of  ap- 
parent solar  days  is  called  a  mean  solar  day  and  is  the  common 
unit  of  time.  It  is  divided  into  two  series  of  12  hours  each,  one 
beginning  at  midnight  and  the  other  at  noon. 

Standard  Time.  —  Before  the  advent  of  railroads  and  the 
telegraph  each  community  used  the  mean  solar  time  of  its  own 
meridian.  As  communication  between  distant  points  became 
frequent  and  rapid,  it  became  necessary  to  have  a  simpler  time 
system.  Hence,  in  1883,  the  railroads  agreed  to  use  a  system 
of  standard  time.  By  this  plan  the  United  States  is  divided 
into  four  time  sections,  each  of  which  uses  the  mean  solar  time 
of  its  standard  meridian.  These  meridians  are  15°  apart  and 
their  times  are  an  hour  apart. 


CHANGE  OF  SEASONS  29 

The  Julian  and  the  Gregorian  Calendars.  —  The  earth  revolves 
around  the  sun  in  about  1 1  minutes  less  than  365I  days. 
Hence  a  calendar  year  of  365  days  is  shorter  than  the  solar 
year.  In  order  to  make  the  calendar  year  more  accurate,  Julius 
Caesar  in  46  B.C.  decreed  that  each  fourth  year  (leap  year) 
should  contain  366  days.  This  correction  was  too  great,  and  in 
1582  the  error  amounted  to  nearly  half  a  month.  In  that  year 
Pope  Gregory  XIII  partially  corrected  the  error  by  suppressing 
10  days  in  the  calendar.  He  also  made  a  rule  which  keeps 
the  calendar  practically  correct.  By  this  rule  every  year  of 
which  the  number  is  divisible  by  4  without  a  remainder  is  a 
leap  year  excepting  years  divisible  by  100,  which  are  leap  years 
only  when  divisible  by  400.  Thus  1600  was  a  leap  year;  1700, 
1800,  and  1900  were  common  years  ;  2000  will  be  a  leap  year  ; 
and  so  on.  The  Gregorian  calendar,  or  New  Style,  was  not 
adopted  in  England  till  1752,  when  Parliament  enacted  that  the 
day  following  September  2  of  that  year  should  be  called  Sep- 
tember 14. 

Change  of  Seasons.  — As  already  shown  (page  26),  when  the 
earth  is  at  A  sunshine  extends  from  pole  to  pole,  and  day  and 
night  are  of  equal  length  everywhere  in  the  world.  As  the 
direct  rays  of  the  sun  at  this  time  fall  upon  the  equator,  the  heat 
there  is  of  the  greatest  intensity,  decreasing  polewards  in  the  two 
hemispheres  as  the  inclination  at  which  they  strike  the  surface 
increases.  This  is  illustrated  on  page  30.  Let  A,  B,  and  C 
represent  three  sunbeams  or  rays  striking  the  earth  in  three 
different  places.  On  account  of  the  remoteness  of  the  sun  they 
are  practically  parallel,  but  owing  to  the  curvature  of  the  earth 
they  are  cut  by  its  surface  at  different  angles.  The  beam  A 
falling  upon  the  equator  warms  an  area  equal  to  its  cross  section ; 
the  beam  B  falling  in  a  latitude  north  of  the  equator  warms  an 
area  of  greater  size  than  its  cross  section,  hence  a  diminished 
temperature  ;  the  beam  C  striking  the  earth  at  a  higher  latitude 
warms  a  still  greater  area,  but  with  a  further  diminution  of  tem- 
perature. There  is,  moreover,  a  loss  in  the  heating  power  of 
the  sun's  rays  occasioned  by  their  passage  through  the  atmos- 


30 


THE   MOTIONS   OF  THE   EARTH 


phere  —  the  more  inclined  the  rays,  the  greater  becomes  the 
atmospheric  distance  to  be  traversed  and  the  greater  the  loss 

of  heat.  (Compare 
the  atmospheric  dis- 
tances traversed  by 
the  beams  A  and  B.) 
The  warming  of 
the  earth  when  in  the 
position  A  (page  26) 
produces  the  condi- 
tions known  as  spring 
in  the  northern  hemi- 
sphere and  autumn 
in  the  southern.  As 
the  earth  advances  in 
its  orbit  toward  B, 
on  account  of  the  in- 
clination of  its  axis 
toward  the  sun,  the 
direct  rays  or  beams 
steadily  move  toward 
the  north  until  at  B 
they  fall  23.^-°  north 
of  the  equator.  The 
Tropic  of  Cancer  is 
therefore  the  northern 
limit  of  the  direct  sun 
rays. 
With  the  increased  length  of  day  in  the  northern  hemisphere, 
which  has  already  been  explained,  comes  an  increase  of  heat 
and  those  conditions  known  as  summer,  while,  on  the  other 
hand,  the  diminution  of  heat  effects,  due  to  the  presence  of  the 
direct  sun  rays  north  of  the  equator  and  the  shortening  of  the  day, 
produce  in  the  southern  hemisphere  the  cold  or  winter  season. 

As  the  earth  moves  toward  the  position  C  in  its  orbit,  the 
direct  rays  of  the  sun  recede  from  the  Tropic  of  Cancer,  the 


Diagram  illustrating  the  Manner  in  which  the 
Sun's  Rays  penetrate  the  Atmosphere  and 
strike  upon  the  Earth's  Surface  in  Differ- 
ent Latitudes 


CHANGE   OF   SEASONS  3 1 

northern  hemisphere  gradually  cools  until  the  conditions  at  A 
are  repeated  ;  that  is,  day  and  night  are  of  equal  length,  the 
direct  rays  fall  upon  the  equator,  and  neither  hemisphere  is 
favored  at  the  expense  of  the  other.  Thus  in  the  northern 
hemisphere  the  summer  season  passes  into  autumn,  while  in  the 
southern  the  wintry  days  have  given  way  to  those  of  spring. 

When  the  earth  has  reached  the  point  D  in  its  orbit,  the  pole 
is  inclined  away  from  the  sun,  and  the  direct  beams  having 
moved  south  of  the  equator  now  fall  23^°  south  of  that  great 
circle.  T/ic  Tropic  of  Capricorn  is  therefore  the  southern  limit 
of  the  direct  sun  rays.  The  summer  of  the  southern  hemi- 
sphere has  arrived  and  the  northern  hemisphere  has  entered 
upon  the  winter  season. 


IV.     TERRESTRIAL   MAGNETISM 

Magnetism  of  the  Earth. — To  the  earth  as  a  whole  belong 
certain  properties  of  a  magneto-electric  character,  not  yet  fully 
understood,  which  are  the  source  of  much  scientific  interest 
as  well  as  of  great  practical  value.  The  importance  of  the 
discovery  of  magnetism  and  the  invention  of  the  compass  can 
scarcely  be  estimated.  Without  that  instrument  navigation 
would  be  practically  impossible  and  the  determination  of  direc- 
tion over  wide  areas  of  the  earth's  surface  futile.  While  mag- 
netism falls  more  properly  within  the  domain  of  physics,  the 
fact  that  the  earth  acts  as  a  weak  magnet  suffices  also  to  bring 
that  subject  within  the  scope  of  physical  geography. 

Magnetism.  —  Among  the  ores  of  iron  there  is  a  variety  of 
the  mineral  magnetite  known  as  lodestone,  which  possesses  the 
power  of  attracting  to  itself  filings  or  other  small  pieces  of  iron. 
Such  a  body  is  called  a  magnet,  and  the  influence  that  it  exerts 
over  other  bodies  is  called  magnetism.  If  a  needle  or  a  bar  of 
steel  be  rubbed  with  lodestone,  this  property  of  the  natural  magnet 
will  be  imparted  to  it,  and  the  needle  or  bar  of  steel  becomes  an 
artificial  magnet.  The  property  of  magnetism  also  appears  in 
a  bar  of  soft  iron  or  steel  forming  the  core  of  an  insulated  coil 
of  copper  wire  through  which  an  electric  current  is  passed,  but 
with  the  cessation  of  the  current  the  magnetic  property  disap- 
pears.    Such  a  temporary  magnet  is  termed  an  electro-magnet. 

Polarity.  —  If  a  bar  magnet  or  a  horseshoe  magnet  be  placed 
beneath  a  sheet  of  paper  upon  which  iron  filings  have  been 
sprinkled  and  the  paper  gently  tapped,  the  iron  particles  will 
arrange  themselves  about  the  extremities  of  the  magnet  in  the 
greatest  abundance,  leaving  the  shape  of  the  magnet  well  out- 
lined upon  the  paper.     The  extremities  of  the  magnet,  where 

32 


THE    EARTH    AS    A    MAGXIT  33 

the  attraction  is  greatest,  are  termed  the  poles,  and  the  area 
through  which  the  magnetic  influence  is  felt,  the  magnetic  field. 
A  comparison  of  the  effects  of  each  pole  upon  the  filings  would 
apparently  lead  to  the  conclusion  that  the  two  poles  are  identi- 
cal, but  a  simple  experiment  will  serve  to  show  that  they  are 
different. 

Let  two  common  needles  be  magnetized  and  each  suspended 
by  a  thread  attached  to  its  middle  point  by  a  bit  of  wax. 
These  needles  will  tend  to  arrange  themselves  in  a  north-and- 
south  direction.  If  their  north  ends  or  poles  be  marked  and 
made  to  approach  each  other,  it  will  be  found  that  between 
them  there  is  exerted  a  repellent  force ;  likewise,  that  between 
the  south  ends  of  the  needles  there  is  also  repulsion.  On  the 
other  hand,  it  may  be  readily  shown  that  between  the  north 
pole  of  one  needle  and  the  south  pole  of  the  other  there  exists 
an  attractive  force.  The  general  law  governing  this  phenom- 
enon is  as  follows  :  Like  poles  repel,  unlike  poles  attract. 

About  halfway  between  the  north  and  south  poles,  along  a 
line  crossing  the  magnet,  the  opposite  magnetic  forces  are  neu- 
tralized.    This  is  known  as  the  nentral  line. 

If  a  piece  of  iron,  or  a  magnetic  needle,  be  suspended  exactly 
over  this  line,  it  will  not  be  attracted  at  all.  On  either  side  of 
it,  however,  a  suspended  needle  is  drawn  toward  one  or  other 
of  the  poles.  The  exact  position  of  the  neutral  line  depends  on 
the  relative  strength  of  the  poles.  As  these  are  seldom  if  ever 
of  equal  strength,  the  neutral  line  will  rarely  or  never  be  equi- 
distant from  both. 

The  Earth  a  Magnet.  —  In  some  very  important  respects  the 
earth  behaves  like  a  magnet. 

In  the  first  place  it  displays  attractive  poiuer  precisely  similar 
to  that  of  the  magnet.  It  is  terrestrial  magnetism  which  causes 
magnets  to  point  northward  when  suspended. 

Secondly,  like  the  magnet,  the  earth  has  magnetic  poles.  These 
are  not  exactly  at  the  north  and  south  geographical  poles,  but  at 
some  distance  from  them.  They  are  the  points  at  which  the 
needle  stands  vertical.     Tht:  north   magnetic  pole  is  in  North 

M.-S.  PHYS,  GEOG.  —  3 


34 


TERRESTRIAL   MAGNETISM 


America.  It  is  situated  in  Boothia,  latitude  70°  5'  nortii,  longi- 
tude 96°  45'  west.  The  discovery  of  this  pole  was  made  by  Sir 
James  Ross  in  1831. 

The  position  of  the 
south  magnetic  pole  has 
not  been  so  accurately 
determined.  Sir  James 
Ross  reached  a  point  in 
the  Antarctic  Ocean  where 
the  inclination  was  88'^  35', 
from  which  its  situation 
has  been  computed.  It  is 
not,  however,  diametrically 
opposite  the  north  mag- 
netic pole,  but  far  to  one 
side.  It  lies  in  the  vicinity 
of  lat.  75°  S.,  long.  138°  E. 
The  positions  of  these 
poles  are  constantly  chan- 
ging- 

Thirdly,  the  earth, 
like  a  magnet,  has  a 
neutral  line.  This 
line  encircles  the 
globe  about  midway 
between  the  north  and 
south  magnetic  poles. 
THE  Earth  as  a  Magnet  Along  it  the  opposite 

The  vertical  arrow  at  the  left  of  the  north  geographic  pole  polar  forceS  Counter- 
points to  the  wcr/// wa^w^/zf /o/^.  The  vertical  arrow  „p^  p'^rYi  other  Tt  is 
at  the  right  of  the  south  geographic  pole  points  from  the 

south  magnetic  pole  (which  is  in  the  hemisphere  turned  Caiied  tne  inClgneilC 
from  the  reader  and  therefore  not  directly  opposite  eOllCltOV.  ItS  COUrse  is 
the  north  magnetic  pole).  ,  ,  ^i         u      ^ 

*  traced  upon  the  chart. 

Inclination  or  Dip  of  the  Needle.  —  In  passing  northward  from 
the  magnetic  equator  the  north  end  of  the  needle  is  drawn 
downward  more  and  more  from  a  horizontal  position  until  the 
north  magnetic  pole  is  reached,  where,  as  already  stated,  it 
points   vertically.      In   like   manner,  in  going    southward   from 


35 


36  TERRESTRIAL   MAGNETISM 

the  magnetic  equator,  the  needle  is  drawn  downward  until 
at  the  south  magnetic  pole  it  should  again  point  vertically, 
although  reversed  in  position.  (On  page  34  the  needle  is  repre- 
sented in  the  form  of  an  arrow.  At  the  north  magnetic  polfe 
the  head  of  the  arrow  is  directed  downward ;  at  the  south  mag- 
netic pole,  the  shaft.) 

Inclination,  or  dip,  may  be  represented  on  a  chart  by  drawing 
lines  in  the  northern  and  southern  hemispheres  connecting  all 
points  in  which  the  atigle  of  dip  is  of  the  same  value. 

Such  lines  are  usually  termed  isoclinic  lines,  but  by  some 
authors  they  have  been  called  magnetic  parallels.  The  line 
connecting  points  having  no  dip  is,  of  course,  the  magnetic 
equator.  In  the  eastern  hemis[)here  it  lies  to  the  north  of  the 
geographic  equator,  but  in  the 'western,  for  the  most  part,  to 
the  south. 

Declination  of  the  Needle.  —  While  magnets  free  to  move  as- 
sume a  north-and-south  direction,  they  do  not  point  exactly  to 
the  true  geographical  north,  but  a  little  to  the  west  or  the  east 
of  it.  The  deviation  from  the  true  northerly  position  is  called 
the  dcclinatioji  of  the  needle. 

The  direction  in  some  places  is  east,  in  others  west.  It  will  be  seen  from 
the  map  that  over  about  one  half  of  the  globe  it  is  easterly,  over  the  other 
half  westerly. 

The  amount  of  declination  varies  in  different  localities,  being 
much  greater  in  some  than  in  others.  This  may  be  presented 
to  the  eye  in  two  ways :  First,  by  drawing  on  the  same  chart 
both  the  true  and  the  magnetic  meridians.  The  latter  have 
been  defined  as  "  the  lines  along  which  one  would  travel  were 
he  to  set  out  at  any  place  on  the  earth  and  always  follow  the 
compass  needle."  As  the  magnetic  poles,  through  which  the 
magnetic  meridians  pass,  do  not  coincide  with  the  geographic 
poles  of  the  earth,  a  greater  or  less  variation  in  the  two  sets  of 
meridians  is  inevitable. 

Second,  by  drawing  lines  on  a  chart  passing  through  those 
places  having  the  same  declination.     Such  lines,  called  isogenic 


U        O 


37 


38  TERRESTRIAL   MAGNETISM 

lines,  must  not  be  confused  with  the  magnetic  meridians.  Just 
as  there  is  a  magnetic  equator  along  which  there  is  no  dip  or 
horizontal  deviation,  so  there  are  lines,  known  as  agonic  lines, 
along  which  there  is  no  declination.  On  the  accompanying 
chart  (page  37)  both  the  isogenic  and  the  agonic  lines  are 
shown.  In  the  western  hemisphere  the  agonic  Une,  passing 
from  the  north  magnetic  pole  southeastward  through  Hudson 
Bay  and  Canada,  enters  the  United  States  near  the  eastern 
end  of  Lake  Superior,  and,  after  traversing  the  intervening 
states  in  a  general  southeast  direction,  leaves  the  country  not 
far  below  the  city  of  Charleston  in  South  Carolina.  Eastward 
of  this  line  the  declination  is  to  the  west ;  westward  of  this  line 
the  decHnation  is  to  the  east.  This  is  indicated  on  the  chart  by 
the  use  of  broken  and  unbroken  lines. 

Variations  in  Declination. —  The  intensity  and  position  of  the 
forces  which  cause  the  needle  to  deviate  from  the  true  north- 
and-south  direction  are  constantly  changing.  Hence  arise  what 
are  known  as  variations  in  declination. 

Secular  variations  extend  over  long  periods.  The  declination  at  London 
was  east  in  1580,  and  amounted  to  11°  15';  in  1657  it  was  zero;  in  1818  it 
attained  its  maximum,  24°  38'  25",  and  was  west.  In  1877  it  had  decreased 
to  19°  22'  22"  west.  It  is  therefore  decreasing  at  the  rate  of  about  5'  an- 
nually ;    so  that  in  about  200  years  it  should  be  east  again. 

Diurnal  variations  also  occur.  They  are  eastward  and  westward  oscillations 
of  the  needle,  caused  every  day  by  the  sun.  The  extreme  eastward  deflection 
is  reached  at  about  8  a.m.,  the  westward  at  about  2  p.m.  The  movements 
observed  at  the  same  hour  in  the  northern  and  southern  hemispheres  are 
opposite  in  direction. 

Diurnal  variation  is  almost  zero  at  the  equator.  In  the  northern  hemi- 
sphere it  is  greatest  at  the  time  of  the  summer  solstice,  least  at  the  winter 
solstice. 

Magnetic  Storms.  —  To  certain  "  spasmodic  variations  "  in  the 
earth's  magnetism,  which  are  plainly  indicated  by  the  behavior 
of  the  needle,  the  term  magnetic  storms  has  been  applied. 
Their  duration  may  vary  from  a  moment  to  several  days. 
Often  they  are  attended  by  electrical  display  such  as  auroras. 
While  their  coming  seems  to  be  somewhat  irregular,  a  relation 


GENERAL  CONCLUSIONS  39 

has  been  noticed  between  these  disturbances  and  solar  activity 
—  that  for  those  years  in  which  the  sun  spots  are  most  numerous 
magnetic  storms  are  most  frequent  and  of  greatest  violence. 
The  "  spot  period  "  of  the  sun  is  a  little  over  eleven  years,  from 
minimum  to  maximum,  say  five  years  ;  from  maximum  to  mini- 
mum, six  years. 

''In  November,  1882,  near  the  period  of  maximum  sun  spots,  a  magnetic 
storm  occurred  which  caused  the  magnetic  needle  at  Los  Angeles,  Cal.,  to 
move  over  i|°  out  of  its  normal  position.  There  was  at  the  time  a  brilliant 
auroral  display.  The  storm  occurred  over  the  entire  earth,  at  Los  Angeles, 
Toronto,  London.  St.  Petersburg,  Bombay,  Hongkong  and  Melbourne,  and 
began  practically  at  the  same  instant  of  absolute  time."' —  L.  A.  Bauer. 

General  Conclusion. —  The  phenomena  above  described  show 
conclusively  that  the  earth  is  a  great  though  rather  feeble  mag- 
net. But  whether  its  magnetism  results  from  magnetic  bodies 
located  within  its  mass  (permanent  magnetism),  or,  as  some 
have  thought,  from  the  generation  of  electric  currents,  due  to 
its  unequal  heating  during  rotation  (electro-magnetism),  is  not 
yet  fully  determined. 

"  All  modern  investigations  would  seem  to  lead  to  the  conclusion  that  there 
exists  both  a  very  deep-seated  magnetic  field  and  one  confined  to  a  compara- 
tively thin  layer,  and  that  the  earth's  total  magnetism  results  from  systems 
of  electric  currents  as  well  as  from  permanent  and  induced  magnetizations." 

—  L.  A.  Bauer. 


V.  INTERNAL  HEAT  OF  THE  EARTH 

Evidences  of  Internal  Heat.  —  While  the  surface  temperature 
of  the  earth's  crust  ranges  from  about  80°  Fahrenheit  at  the 
equator  to  possibly  0°  F.  at  the  poles,  there  are  good  reasons  for 
believing  that  the  earth's  interior  is  intensely  hot.  As  bearing 
upon  this  subject  the  evidence  furnished  by  deep  mines,  hot 
springs,  geysers  and  artesian  wells,  and  volcanoes  will  be  con- 
sidered. 

Mines.  —  In  his  search  for  mineral  wealth  man  has  penetrated 
far  into  the  earth's  crust.  In  many  parts  of  the  world  his 
operations  have  been  carried  on  by  means  of  deep  shafts,  and 
in  no  instance  has  he  failed  to  note  an  increase  of  temperature 
for  an  increase  of  depth  below  the  surface.  A  comparison  of 
observations  made  in  widely  separated  localities  shows  that  the 
rate  of  increase  is  not  altogether  uniform,  but  varies  with  the  con- 
ductivity, or  power  to  transmit  heat,  of  the  rocks  encountered, 
and  is,  moreover,  modified  by  local, conditions,  as  proximity  to  a 
volcano  or  a  mass  of  igneous  rock  not  yet  thoroughly  cooled. 

Omitting  exceptional  cases,  the  average  rate  of  increase,  for 
depth  below  the  line  unaffected  by  surface  heat  or  cold  (line  of 
no  variation),  seems  to  be  1°  F.  for  about  65  feet. 

In  boring  the  Saint  Gothard  tunnel,  between  Italy  and  Switzerland,  the 
temperature  increased  at  the  rate  of  1°  F.  for  82  feet,  and  in  boring  the  Mont 
Cenis  tunnel,  between  Italy  and  France,  at  the  rate  of  1°  F.  for  79  feet. 

As  illustrating  the  extremes  of  variability  two  unusual  cases  may  be  cited. 
As  the  result  of  careful  observation  at  the  celebrated  Calumet-Hecla  copper 
mine  on  the  south  shore  of  Lake  Superior,  it  has  been  found  that  for  the  depth 
of  4939  feet  the  average  increase  of  temperature  is  1°  F.  for  103  feet. 

On  the  other  hand,  unusually  high  temperatures  have  been  experienced 
at  the  Comstock  lode,  Virginia  City,  Nev.,  as,  for  example,  130°  F.  at  the 
depth  of  2000  feet  or  an  increase  of  1°  F.  for  15.4  feet  of  descent,  and  at  the 
Gold  Hill  mines  on  the   same  lode  waters  entered  the  3000-foot  level  at  a 

40 


HOT   SPRINGS  41 

temperature  of  170^  F.,  which  would  give  an  average  of  1°  F.  for  28  feet. 
These  high  temperatures  may  be  due  to  the  decomposition  of  rocks  contain- 
ing feldspar. 

Artesian  Wells  bear  testimony  to  the  same  rapid  increase  of 
heat.  These  have  been  sunk  in  various  parts  of  Europe  and 
America  to  a  depth  varying  from  1000  104000  feet. 

The  rate  of  increase  in  the  temperature  varies  in  different 
places.  The  average  is  1°  F.  for  50  to  70  feet.  The  temperature 
of  the  well  at  Grenelle,  near  Paris,  is  81.7°  F.  Its  depth  is  1798 
feet.  That  at  Budapest  is  3160  feet  deep.  Its  temperature 
is  178°  F.  It  supplies  a  part  of  the  city  with  warm  water. 
An  artesian  well  at  Marlin,  Tex.,  3330  feet  in  depth,  has  a 
temperature  of  147°  F. 

Experience  shows  that  by  boring  artesian  wells,  warm  water 
may  be  obtained  in  almost  every  region  of  the  earth. 

Hot  Springs.  —  Hot  or  ///^rw/rt/ springs  occur  in  all  parts  of  the 
world.  While  more  abundant  in  volcanic  regions,  they  are  by 
no  means  confined  to  the  vicinity  of  volcanoes.  The  thermal 
springs  of  Bath,  England,  having  a  mean  temperature  of  120°, 
are  900  miles  from  the  Icelandic  volcanoes,  over  1000  miles 
from  Vesuvius  and  Etna,  and  fully  400  miles  from  the  extinct 
volcanic  region  of  France. 

As  to  the  source  of  the  heat  manifested  by  hot  springs  there 
is  reason  to  believe  in  many  instances  that  it  is  local,  as  in  the 
case  of  springs  occurring  in  regions  of  active  and  extinct  vol- 
canoes. There  are,  however,  thermal  springs,  breaking  out 
along  the  line  of  deep  fissures,  in  which  the  source  must  be 
regarded  as  "deep-seated,"  and  there  are  still  other  cases  in 
which  chemical  action  may  be  urged  as  the  source  of  heat. 
Hot  springs,  it  seems,  afford  evidence  of  the  existence  of  sub- 
terranean heat,  but  they  furnish  meager  data  for  establishing 
its  rate  of  increase  for  depths  below  the  surface. 

On  the  Island  of  Saint  Michael,  one  of  the  Azores,  there  are  .some  remarkable 
hot  springs.  Here  the  waters  rising  through  volcanic  rocks  become  charged 
with  silica  (the  substance  of  quartz),  which,  upon  reaching  the  .surface,  on  ac- 
count of  cooling,  they  precipitate,  or  deposit,  in  the  form  of  sinter.     As  these 


42 


INTERNAL  HEAT  OF  THE  EARTH 


waters  act  as  a  petrifying  medium,  grasses,  ferns,  and  other  forms  of  vegetation 
are  seen  about  the  basins  in  various  stages  of  minerahzation. 

An  excellent  example  of  the  deposit  of  carbonate  of  Hme  is  afforded  by  the 
terraces  of  Mammoth  Hot  Springs,  Yellowstone  National  Park.  It  is  thought 
that  the  precipitation  here  may  in  part  be  due  to  the  action  of  algae  (low 
forms  of  plant  life),  to  which  also  may  be  attributed  the  brilliant  colorings, 
scarlet,  blue,  green,  noticed  upon  freshly  forming  surfaces. 

Geysers.  —  The  term  geysers  or  gushers  is  applied  to  certain 
periodically  eruptive  hot  springs  occurring  in  limited  areas  in 


Minerva  Terrace,  a  Hot  Spring  Deposit,  Yellowstone  National  Park 
The  substance  of  this  beautiful  terrace  is  travertine  or  carbonate  of  lime.     By  its  deposi- 
tion from  hot  waters  numerous  basins  have  been  built  up  which  now  contain  pools  of 
various  temperatures.     From  photograph  by  Haynes. 

regions  of  active  or  dying  volcanic  energy.  The  most  noted 
are  those  of  the  Yellowstone  National  Park  in  northwestern 
Wyoming,  Iceland,  and  New  Zealand. 

The  distinguishing  characteristic  of  a  geyser  is  an  eruption 
during  which  hot  water  and  steam  are  ejected  with  more  or  less 
violence  from  a  craterlike  opening  or  basin  which  is  connected 
below  with  a  pipe  or  conduit  leading  downward  into  the  earth. 
The  water  is  heated  to  a  high  temperature ;  that  of  the  Great 
Geyser  in  Iceland  is  212°  F.  at  the  surface,  but  in  the  lower 


VOLCANOES  43 

portion  of  the  tube  the  thermometer  indicates  266°.  By  the 
relief  of  pressure,  due  to  the  overflow  of  the  basin,  the  super- 
heated waters  rising  toward  the  surface  suddenly  flash  into 
steam,  thus  producing  an  explosion  or  eruption  by  which  a 
column  of  water  and  steam  is  projected  far  above  the  vent. 

Like  ordinary  hot  springs,  geysers  afford  evidence  of  the 
existence  of  heat  below  the  earth's  surface,  but  the  source  of 
the  heat  is  evidently  volcanic. 

About  the  mouths  of  geysers  there  are  often  found  highly  ornamental  incrusta- 
tions, consisting  of  silica  and  other  minerals  which  are  soluble  in  the  geyser 
water  while  it  is  hot,  but  are  deposited  as  it  cools.  The  basins  or  craters  vary 
in  size  from  a  few  inches  to  many  feet  in  diameter  and  height.  That  of  the 
Great  Geyser  in  Iceland  is  four  feet  in  depth  and  72  feet  in  diameter.  In  the 
center  of  this  basin  is  a  pipe  or  funnel  eight  feet  wide.  Out  of  this  funnel 
water  nearly  boiling  constantly  issues.  Eruptive  discharges  also  occur.  Of 
these  there  are  certain  premonitions.  Underground  rumblings  are  heard, 
the  water  in  the  basin  boils  furiously,  and  a  domelike  mass  of  hot  water  with 
clouds  of  steam  is  thrown  40  or  50  feet  high. 

One  or  more  of  these  minor  discharges  occur,  and  then  succeeds  a  grand 
eruption.  With  a  rumbling  that  shakes  the  ground,  another  column  of 
boiling  water  90  to  100  feet  high  is  forced  into  the  air  with  loud  explosions 
and  amid  clouds  of  steam.  Then  out  through  the  top  of  this  column  smaller 
jets  are  driven  to  marvelous  heights  above  it.  The  pipe  is  thus  emptied  of 
water.  But  at  once  it  begins  to  fill  up,  only  to  be  emptied  again  by  another 
grand  explosion. 

Of  the  Yellowstone  geysers  an  observer  says  t  — 

"  Of  all  the  geysers  whose  eruptions  v/e  witnessed,  the  Grand  was,  I  think, 
the  most  interesting.  It  played  each  evening  at  a  regular  hour.  Suddenly 
it  shot  a  vast  stream  of  water  over  200  feet  into  the  air.  This  was  maintained 
for  a  few  minutes ;  then  it  ceased,  and  the  wafers  shrank  back  into  the  cav- 
ernous hollow  below.  Meanwhile  subterranean  thunder  shook  the  ground, 
and  after  a  minute's  cessation  another  eruption  occurred." 

Volcanoes  are  the  most  striking  of  all  manifestations  of  the 
earth's  internal  heat.  They  are  so  important  that  they  will 
be  considered  in  detail  in  a  subsequent  lesson.  Here,  however, 
it  is  proper  to  observe  what  strong  confirmation  they  afford  to 
the  theory  of  subterranean  heat.  Streams  of  lava,  white-hot, 
like  molten  iron,  issue  through  their  craters  from  the  interior  of 


44 


INTERNAL  HEAT  OF  THE  EARTH 


A  Geyser  in  Eruption 

"  Old  Faithful,"  Yellowstone  National  Park.  This  celebrated  geyser  received  its  name 
from  the  regularity  of  its  eruptions,  which  occur  at  intervals  averaging  65  minutes. 
The  discharge  lasts  five  or  six  minutes,  the  column  of  steam  and  water  reaching  the 
height  of  90  to  100  feet.     From  photograph  by  Haynes. 


CONDITION   OF  THP:    INTERIOR   OF  THE   EARTH  45 

the  earth,  together  with  steam  and  other  heated  vapors,  hot 
ashes,  and  stones. 

Condition  of  the  Interior  of  the  Earth.  —  The  phenomena 
above  considered  have  suggested  the  conchision  that  the  inte- 
rior of  the  earth  is  in  a  fluid  state  and  that  only  to  the  depth  of 
from  30  to  40  miles  is  the  crust  of  the  earth  solid. 

It  is  argued  that  if  the  heat  increase  for  depths  below  the 
surface  at  the  rate  noted  in  mines  and  deep  borings,  then  at 
a  comparatively  shallow  depth  even  the  most  refractory  sub- 
stances must  necessarily  be  in  a  state  of  fusion.  This  view,  it 
will  be  observed,  is  in  accord  with  the  nebular  hypothesis. 

Most  scientific  men,  however,  doubt  the  fluidity  of  the  central 
mass,  and  admit  the  existence  only  of  local  reservoirs  of  molten 
rock.  They  contend  that,  instead  of  being  fluid,  the  interior  of 
the  earth,  though  intensely  hot,  is  pasty,  or  even  solid.  In 
support  of  this  they  argue  that  the  enormous  pressure  exerted 
upon  the  interior  of  the  earth  would  nullify  the  effect  of  its 
internal  heat;  for  if  a  substance  be  subjected  to  pressure,  it  can- 
not melt  so  readily  as  under  ordinary  conditions.  A  body, 
therefore,  may  remain  solid  at  a  very  high  temperature,  if  under 
pressure.*  In  consequence  of  this  the  state  of  the  successive 
layers  constituting  the  earth  is  such  that  while  they  are  sub- 
jected to  a  heat  which  increases  enormously  as  the  center  is 
approached,  they  are  at  the  same  time  subjected  to  a  presstire 
which  also  increases  enormously  as  the  center  is  approached. 

Whether,  however,  we  adopt  the  view  that  the  central  mass 
is  fluid  or  solid,  it  does  not  affect  the  conclusion  that  it  is  in  an 
intensely  heated  condition. 

*  This  is  applicable  to  substances  which  contract  when  they  solidify  ;  ice  and  a 
few  other  substances,  which  expand  upon  solidification,  have  their  melting  points 
lowered  by  pressure. 


VI.    VOLCANOES 

What  is  a  Volcano  ?  —  To  this  question  there  are  two  answers: 
The  first  is  that  of  the  geographer;  the  second,  that  of  the 
geologist. 

(i)  The  term  volcano  is  usually  applied  to  a  mound,  hill,  or 
mountain  composed  of  rocky  materials  ("  lava,"  "  cinders," 
"ashes,"  etc.)  ejected  from  the  earth's  interior  through  a  tube 
or  opening  in  the  crust.  The  upper  end  of  this  conduit  is  in 
a  bowl-shaped  depression,  called  a  crater,  which  may  be  on  the 
summit  or  slope  of  the  ejected  mass.  As  typical  volcanoes  are 
ordinarily  more  or  less  conical,  it  is  customary  to  speak  of  vol- 
canic cones. 

(2)  But  as  defined  by  Professor  Judd,  volcanoes  are  not  neces- 
sarily "mountains"  at  all.  "Essentially  they  are  just  the  re- 
verse —  namely,  holes  in  the  earth's  crust,  or  outer  portion,  by 
means  of  which  communication  is  kept  up  between  the  surface 
and  the  interior  of  our  globe." 

Kilauea,  on  an  island  of  the  Hawaiian  group  in  the  North  Pacific  Ocean,  on 
account  of  the  great  size  of  its  crater,  is  one  of  the  most  remarkable  volcanoes 
of  the  world.  Its  external  opening,  on  the  flanks  of  Mauna  Loa,  is  in  the 
form  of  a  basin  nearly  1000  feet  deep.  This  great  crater  has  a  width  of  two 
miles,  a  length  of  three  miles,  and  a  circumference  of  eight  miles. 

Formation  of  Volcanic  Cones.  —  If  at  its  beginning  a  volcano  is 
simply  a  hole  in  the  earth's  crust,  the  form  assumed  by  the 
cone  will  depend  very  much  upon  the  character  of  the  material 
ejected.  Should  it  be  in  a  very  Hquid  state,  like  melted  glass 
or  iron,  then  the  cone  will  rise  at  a  low  angle  from  a  spreading 
base  as  seen  in  the  Hawaiian  volcanoes.  Should,  however,  the 
material  be  viscous,  like  pitch,  the  cone  will  rise  at  a  steeper 
angle  and  will  assume   somewhat  of  a  dome   shape.     Again, 

46 


HEIGHT   OF   VOLCANIC   CONES 


47 


should  the  material  ejected  be  fragmental,  as  ashes  and  cin- 
ders, the  cone  will  rise  at  a  rather  high  angle  and  take  on 
the  form  seen  in  Cotopaxi  and  Chimborazo.  The  inclination 
or  slope  of  a  mixed  cone,  that  consisting  of  both  molten  and 
fragmental  materials  ejected  from  the  same  vent,  will,  in  large 
degree,  depend  upon  the  kind  of  material  predominating,  being 
steeper  for  the  fragmental  and  less  steep  for  the  molten. 

Submarine  Volcanoes.  —  The  formation  of  a  volcano  may  begin 
at  considerable  depths  below  the  level  of  the  sea.  In  proof  of 
this  it  may  be  said  that  vast  numbers  of  oceanic  islands  owe 
their  existence  to  volcanic  action,  and  deep-sea  soundings  show 
that  many  of  the  deepest  parts  of  the  ocean  are  covered  with 
volcanic  debris. 

In  1 83 1  a  mass  of  matter  accompanied  by  a  discharge  of  steam  rose  from 
the  sea  near  the  coast  of  Sicily,  and  attained  in  a  few  weeks  the  height  of  200 
feet  above  the  water.  It  had  a  circumference  of  about  three  miles  and  was  named 
Graham  Island.  In  a  few  months,  however,  it  disappeared,  as  the  materials 
composing  it,  being  loosely  held  together,  were  unable  to  withstand  the 
action  of  the  waves. 

Height  of  Volcanic  Cones.  —  Volcanic  cones  vary  much  in 
height.     Some   are   but   slightly  elevated,  less  than    500  feet ; 


1        .fl^_ 

1 

ij^^^g 

'^^-^SSS**^^^*^':.^;^ 

HHB^^^i^'^ 

Small  Co.nl  nlar  Ul ter  Rlm  of  Mau.na  Loa 

Others  tower  skyward  many  thousand  feet.  The  latter  do  not 
attain  this  great  height  through  the  accumulation  of  ejected 
matter  alone,  but  are  usually  situated  in  highly  elevated  plateau 
or  mountainous  regions,  as  is  conspicuously  shown  in  the  case 


48 


VOLCANOES 


of  the   higher  volcanoes  of  the   Andes.     Here  are  cones  like 
Aconcagua,  in  Chile,  and  Chimborazo,   in    Equador,   attaining 


! 

i^ggg^-^^A^^^^ 

■F^ 

^^SJ 

'^iS 

^Jai^ 

MaUNA    KEA,   the    HlCHEST    MOUNTAIN    IN   THE   PACIFIC    {13,805   feet) 

an  elevation  of  over  20,000  feet.  Mount  Vesuvius,  the  best- 
known  volcano  of  the  world,  has  an  altitude  of  about  4000 
feet,  while  Mauna  Kea,  in  the  Hawaiian  Islands,  reaches  13,805 

feet. 


Lava  Flows  on  Mauna  Loa 
Smooth  lava,  known  as  pahoehoe,  on  the  left;  granular  lava  on  the  right. 

Volcanic  Products.  —  The    materials  ejected   from  volcanoes 
are  steam  and  other  gases,  lava,  stones,  ash,  sand,  and  dust. 
Of  all  the  vapors  given  off  during  an  eruption  steam  is  by 


VOLCANU     I'RODUCTS 


49 


far  the  most  abundant.  This  when  chilled  hovers  above  the 
vent  in  the  form  of  a  great  cloud  which  upon  further  conden- 
sation falls  as  rain.  The  steam  discharge  is  especially  violent 
during  an  eruption  of   the   explosive   type.     Steam   and   other 

volatile  substances  often  escape  from  fissures  and   minor  A'cnts. 


Lava  Cascade,  Kilauea 

within  the  crater,  called  fumaroles,  as  well  as  from  e.xternal 
fissures  and  even  from  flowing  lava. 

Of  the  volcanic  gases  the  following  may  be  mentioned:  hydro- 
chloric acid,  sulphureted  hydrogen,  sulphurous  acid,  and  carbon 
dioxide. 

To  the  molten  product  of  volcanic  action  the  term  lava  has 

.M.-s.  pjivs.  geck;.  —  4 


50  VOLCANOES 

been  applied.  In  its  consistency  and  appearance  it  is  subject 
to  a  wide  range.  It  may  be  thin  and  free  flowing  when  erupted, 
or  it  may  be  ropy  and  viscid  ;  it  may  be  highly  charged  with 
steam  or  other  vapor,  which  expanding  imparts  a  cellular  struc- 
ture, or  it  may  be  rather  compact ;  it  may  be  very  light  colored 
or  it  may  be  very  dark  —  ranging  from  almost  white  through 
gray,  brown,  and  even  red,  to  black.  In  general  it  has  the 
appearance  of  slag  as  seen  about  a  smelting  furnace. 

An  exceedingly  cellular  form  of  lava,  the  consolidated  froth, 
forms  what  is  known  as  pumice  or  pumice  stone.  Often  lava 
is  reduced  to  fragments  so  fine  as  to  form  dust  or  asJi;  or,  if 
the  particles  are  coarser,  volcanic  sand.  Again,  molten  lava, 
of  the  highly  liquid  variety,  is  sometimes,  either  by  the  action 
of  escaping  steam  or  by  the  blowing  of  the  wind,  drawn  out 
into  long,  delicate  fibers,  like  spun  glass,  called  by  the  native 
Hawaiians  "  Pele's  hair  "  in  honor  of  the  goddess  of  Kilauea, 

Volcanoes  Classified.  — Volcanoes  may  be  classified  as  active, 
dormant,  or  extinct.  Active  volcanoes  eject  various  substances. 
When  no  signs  of  activity  are  given  for  a  considerable  time,  the 
volcano  is  said  to  be  dormant.  When  a  volcano  has  been  dor- 
mant for  centuries,  and  it  seems  probable  that  its  activity  is  lost 
forever,  it  is  said  to  be  extinct. 

The  frequency  of  volcanic  discharges  is  varied.  Some  vol- 
canoes are  continuously  active.  Stromboli  has  been  for  2000 
years  in  a  state  of  constant  but  not  dangerous  activity.  It  is 
visible  at  night  in  every  direction  for  the  distance  of  more  than 
100  miles.  A  red  glow  is  seen  from  time  to  time  above  the 
summit  of  the  mountain  due  to  the  illumination  of  the  vapor 
cloud  by  the  red-hot  lava  in  the  crater.  This  becomes  gradu- 
ally more  and  more  brilliant,  and  then  as  gradually  dies  away. 
It  is  this  phenomenon  which  has  given  to  Stromboli  the  name 
"  Lighthouse  of  the  Mediterranean." 

On  the  other  hand,  Cotopaxi  has  been  in  eruption  only  seven 
times  in  100  years. 

Vesuvius  exhibits  great  irregularity.  It  had  been  long  dormant  previous  to 
the  eruption  of  a.d.  79,  and  the  steep  walls  of  its  crater  were  covered  with 


ERUPTIONS 


51 


vines  and  other  vegetation.  Cities  and  villages  graced  its  slopes.  After  this 
eruption,  none  of  great  moment  occurred  until  1631.  At  that  time,  one  of  the 
most  destructive  on  record  took  place.  It  continued  for  three  months,  and 
destroyed  a  number  of  cities  and  villages.  The  last  eruption  occurred  in  April, 
1906. 

From  these  and  similar  facts  it  is  evident  that  we  have  no 
knowledge  of  any  law  which  governs  the  frequency  of  volcanic 
eruptions. 

Eruptions.  —  The  character  of  volcanic  eruptions  is,  in  a 
great  measure,  dependent  upon   the    nature    of   the    materials 


Vesuvius  in  Eruption,  April  5,  1906 
A  dense  column  of  steam  and  ashes  is  rising  from  the  crater.     The  steam  below  the  sum- 
mit is  from  a  recent  lava  fiow.    See  also  Frontispiece. 

ejected.  The  emission  of  great  bodies  of  steam  and  other  gases 
is  productive  of  an  eruption  of  an  explosive  type,  which  is  usually 
accompanied  by  a  discharge  of  fragmentary  matter  of  various 
kinds,  such  as  dust,  ash,  and  even  blocks  of  lava.  On  the  other 
hand,  when  the  emission  consists  mainly  of    molten  lava,  the 


52 


VOLCANOES 


eruption  is  less  violent,  or  of  the  quiet  type.  Many  of  the  best- 
known  volcanoes  discharge  matter  in  the  gaseous,  liquid,  and 
solid  forms,  their  eruptions  being  of  a  mixed  type. 

Eruptions  are  usually  preceded  by  subterranean  rumblings 
and  tremors.  Before  the  great  eruption  of  1872,  Vesuvius  gave 
indications  of  unusual  activity  for  a  whole  year.  In  many 
cases,  however,  the  eruption  follows  the  warning  immediately. 
An  eyewitness,  writing  of  Stromboli,  says  that  he  had  observed 
numerous  light,  curling  wreaths  of  vapor  ascending  from  the 
crater,  then  suddenly,  without  the  slightest  warning,  a  sound 
was  heard  like  that  of  a  locomotive  giving  off  steam ;  and  the 
eruption  at  once  occurred. 

In  general,  after  the  preliminary  rumblings  and  tremors, 
dense  columns  and  globular  masses  of  watery  vapor  mingled 
with  a  variety  of  gaseous  substances  issue  from  the  crater. 
According  to  the  state  of  the  atmosphere,  and  the  existence  of 
winds  and  air  currents,  the  vapor  assumes  a  variety  of  forms. 

In  the  case  of  Mount  Vesuvius  it  not  unfrequently  expands 
after  attaining  a  certain  height,  and  becomes  like  a  vast  "  um- 
brella," as  the  Italians  call  it,  having  a  top  many  miles  in  cir- 
cumference. The  lurid  glare  of  the  boiling  lava  in  the  crater 
below  is  reflected  upon  the  under  surface  of  the  umbrella,  and 
gives  the  appearance  of  a  vast  conflagration.  This  spectacle 
is  indescribably  impressive  at  night.  During  a  great  eruption 
of  Vesuvius,  vapor,  it  is  said,  rose  to  the  height  of  20,000  feet, 
or  nearly  four  miles. 

The  steam  emitted,  being  condensed,  falls  as  rain.  This 
rainfall  is  excessive  and  long  continued,  and  often  gives  rise  to 
destructive  floods.  Around  the  vapory  column  vivid  lightning 
constantly  plays. 

Jets  of  steam  under  high  pressure,  if  allowed  to  issue  from  an  orifice,  give 
rise,  in  doing  so,  to  large  quantities  of  electricity.  A  machine  has  been  con- 
structed to  generate  electricity  in  this  way.  From  it  torrents  of  sparks  as 
much  as  14  inches  in  length  have  been  obtained.  The  crater,  with  its 
immense  volume  of  uprising  vapor,  may  be  compared  to  a  gigantic  machine 
of  this  description. 


ERUPTIONS 


53 


Often  with  the  vapor  are  mingled  immense  quantities  of  vol- 
canic as/ies  and  sand,  which  descend  and  cover  the  surrounding 
country,  sometimes  to  the  depth  of  many  feet. 

Over  1800  years  ago  (a.d.  79),  the  cities  of  Herculaneum 
and  Pompeii  in  Italy  were  covered  with  a  deluge  of  ashes 
from    an    eruption  of   Vesuvius.     They  were    buried  from    70 


Fuji,  a  Volcanic  Peak,  Japan 
The  highest  mountain  in  Japan  (altitude  about  12,400  ft.). 


to  120  feet,  and  lost  to  view  for  nearly  seventeen  centuries. 
In  1 71 3,  a  well  digger  turned  up  a  bit  of  statuary,  which  led  to 
the  discovery  of  the  two  cities.  The  work  of  exhuming  them  is 
still  going  on. 

The  distance  to  which  the  ashes  of  a  volcano  may  be  carried  is  ahiiost 
incredible.  In  1845,  the  ashes  of  Hecla  were  carried  to  the  Orkney  Islands, 
a  distance  of  nearly  700  miles,  and  in  181 5,  those  of  Tomboro,  in  the  island 
of  Sumbawa,  fell  at  Benkulcn,  iioo  miles  away. 


54  VOLCANOES 

In  August,  1883,  during  an  explosive  eruption  on  the  island  of  Krakatoa, 
situated  in  the  Straits  of  Sunda,  an  immense  volume  of  dust  amounting  to  42 
cubic  miles  was  suddenly  hurled  upward  into  the  atmosphere.  This  great 
dust  cloud  attained  a  probable  height  of  17,000  feet,  and  so  fine  were  its  com- 
ponent particles  that  they  remained  suspended  for  many  months  in  the  upper 
air,  giving  rise,  it  is  thought,  to  an  interesting  optical  phenomenon  known  as 
the  *'  red  sunsets.''. 

During  the  disastrous  outbreak  of  Mont  Pelee,  on  the 
island  of  Martinique,  in  May,  1902,  an  immense  quantity  of 
superheated  steam  and  acid  vapor  charged  with  incandesce9it 
lava  fragments,  in  the  form  of  dust,  sand,  and  stones,  rolled 
down  the  mountain  side,  destroying  almost  instantly  the  town 
of  Saint  Pierre  and  its  30,000  inhabitants. 

The  Emission  of  Lava  in  the  molten  state  is  the  most  impos- 
ing of  volcanic  phenomena.  The  action  which  goes  on  has 
been  compared  to  that  which  occurs  in  a  pot  of  boiling  por- 
ridge. 

As  the  mass  of  porridge  is  heated,  steam  is  generated  at  the  bottom.  This 
rises  through  the  porridge.  In  doing  so  it  forces  a  portion  upward.  More 
and  more  steam  being  generated,  bubbles  of  porridge  rise  to  the  surface,  and 
mimic  explosions  occur,  or  the  porridge  is  thrown  in  little  jets  above  the 
surface  of  the  boiling  material.  The  process  may  increase  in  violence  until 
the  phenomenon  of  boiling-over  takes  place.  Quite  similarly  the  boiling  lava 
is  forced  upward  higher  and  higher  in  its  crater  by  vast  volumes  of  steam  that 
are  seeking  to  escape.  Explosions  occur  on  the  boiling  surface,  and  often  jets 
are  thrown  far  into  the  air. 

Finally,  the  rising  lava  overflows  the  rim  of  the  crater,  or  quite  as  often 
bursts  through  the  sides  of  the  mountain,  and  pours  down  its  slopes  in  rivers 
of  fire. 

So  numerous  were  the  fissures  which  rent  Vesuvius  in  the  eruption  of  1872 
that  liquid  lava  seemed  to  ooze  from  every  portion  of  it,  and,  as  an  eye- 
witness expressed  it,  "  Vesuvius  sweated  fire." 

Lava  streams  vary  in  magnitude.  The  largest  recorded  were 
those  of  Skaptar  Jokul,  in  Iceland,  in  the  years  1783-85.  Tor- 
rents of  molten  rock  deluged  the  island.  River  courses,  ravines, 
and  lakes  were  filled,  and  the  surface  of  the  country  for  hun- 
dreds of  square  miles  was  completely  devastated.  Some  of  the 
streams  were  about  50  miles  in  length,  and  in  certain   places 


DISTRIBUTION   OF   VOLCANOES  55 

15  miles  in  breadth,  and  100  feet  deep.  In  some  of  the  narrow 
valleys  the  depth  was  600  feet. 

The  velocity  of  the  streams,  and  the  distance  to  which  they 
reath,  depend  on  the  fluidity  of  the  lava  and  the  slope  of  the 
land.  One  thousand  feet  per  hour  is  a  rapid  rate  ;  the  extreme 
of  10,000  feet  per  hour  has  been  observed,  though  rarely. 

The  retention  of  its  heat  by  a  lava  stream  is  very  remarkable. 
When  the  surface  of  the  stream  has  cooled,  it  becomes  a  hard 
crust  which  prevents  the  rapid  escape  of  the  heat. 

A  mass  of  lava  500  feet  thick,  ejected  from  Jorullo  in  1759,  was  seen  smok- 
ing by  Alexander  von  Humboldt  45  years  after.  The  Indians  lit  cigars  at  its 
crevices.  The  lava  thrown  from  Vesuvius  in  1858  continued  as  late  as  1873 
to  give  out  steam,  and  remained  so  hot  that  one's  hand  could  not  be  held  in 
some  of  the  fissures  for  more  than  a  few  seconds. 

The  flow  of  the  lava  is  the  beginning  of  the  end.  After  its 
occurrence  the  showers  of  ashes  gradually  cease,  the  explosions 
become  less  and  less  frequent,  and  at  length  no  evidence  of 
volcanic  activity  remains,  save  perhaps  a  vapor  cloud  veiling  the 
summit  of  the  mountain. 

Distribution  of  Volcanoes. — Two  significant  facts  are  to  be 
observed  regarding  the  distribution  of  volcanoes. 

First :  The  active  volcanoes  of  the  globe  are,  as  a  rule,  situ- 
ated upon  areas  which  are  undergoing  upheaval.  Those  por- 
tions of  the  surface  of  the  earth  which  are  subsiding  are  without 
volcanic  activity. 

Second  :  Almost  all  volcanoes  are  near  the  sea.  Those  upon 
the  continents  are  close  to  the  shores.  The  only  well-authen- 
ticated examples  of  volcanoes  situated  far  inland  are  those  of 
Ararat  and  Demavend,  of  Peshan  and  Turfan,  or  Hot-Scheou, 
and  the  Solfatara  of  Urumtsi,  all  in  Central  Asia. 

The  most  striking  exemplification  of  this  law  of  volcanic  distribution  is 
presented  by  the  Pacific  Ocean.     It  is  literally  encircled  with  active  volcanoes. 

There  are  three  great  belts  traversing  the  globe,  within  which 
nearly  all  the  volcanoes  of  the  world  are  situated.  These  may 
be  called  the  Pacific  Insular  Belt,  the  Atlantic  Insular  Belt,  and 
the  American  Continental  Belt.     (See  map  on  p.  57.) 


56  VOLCANOES 

The  Pacific  Insular  Belt  extends  along  the  northern  and  west- 
ern shores  of  the  Pacific  Ocean.  Beginning  with  the  Aleutian 
Islands  it  embraces  Kamchatka,  the  Kurile,  Japanese,  and  Philip- 
pine Islands,  Sumatra,  Java,  New  Guinea,  the  Tonga  Islands, 
and  New  Zealand. 

One  extension  of  this  belt  embraces  the  Society,  Marquesas,  and  Sandwich 
or  Hawaiian  Islands ;  another  is  the  volcanic  region  of  Victoria  Land. 

The  Atlantic  Insular  Belt  comprises  extinct  and  active  vol- 
canoes and  volcanic  islands  which  traverse  the  Atlantic  from 
north  to  south.  The  islands  of  Jan  Mayen,  Iceland,  the  Azores, 
Cape  Verde  Islands,  Saint  Helena,  and  Tristan  da  Cunha  are 
points  which  mark  this  volcanic  band. 

The  American  Continental  Belt  extends  from  Cape  Horn  and 
the  South  Shetland  Islands  to  Alaska,  a  distance  of  more 
than  10,000  miles.  All  along  this  line  volcanoes,  singly  or  in 
groups,  are  found.  An  outlying  spur  of  it  includes  the  Lesser 
Antilles. 

A  minor  yet  very  important  volcanic  belt  is  that  of  the  Mediterranean 
region.  It  comprises  Etna,  Vesuvius,  Stromboli,  and  Vulcano  in  the  Lipari 
Islands,  and  Santorini  and  Nisyros  in  the  ^gean  Sea. 

Outside  of  the  three  great  belts  there  are  many  volcanoes 
irregularly  distributed.  In  the  Pacific  all  islands  not  of  coral 
origin  are  composed  of  volcanic  rocks.  In  the  Indian  Ocean 
there  are  volcanoes  upon  Madagascar  and  the  adjacent  islands. 

In  central  France,  in  Spain,  and  generally  throughout  Europe, 
there  are  numberless  proofs  of  volcanic  action.  The  volcanoes 
most  remarkable  for  the  irregularity  of  their  situation  are  those 
in  Central  Asia  already  mentioned. 

The  number  of  active  volcanoes  on  the  surface  of  the  globe 
is  estimated  at  from  300  to  350.  Of  dormant  and  extinct  about 
1000  are  reckoned. 

Volcanoes  of  the  Malay  Archipelago.  —  No  other  region  in  the 
world  is  so  thickly  studded  with  volcanic  cones  as  that  of  the 
Malay  Archipelago,  of  which  Java  is  the  center.  On  that  island 
alone  they  number  between  20  and  30.     Their  discharge,  how- 


DlSTRlBUriON    OF    VOLCANOES 


57 


Chart  showing  the  Distribution  of  Volcanoks 


58  VOLCANOES 

ever,  is  not  usually  lava,  but  sulphurous  vapors,  acid  waters,  and 
mud.  Occasionally  in  this  region  there  are  eruptions  of  the 
explosive  type  on  a  stupendous  scale,  as  that  of  Papandayang, 
Java,  in  1772,  Tomboro,  Surnbavva,  in  181 5,  and  on  the  island  of 
Krakatoa  in  1883. 

During  the  famous  eruption  of  Papandayang  its  cone  lost  4000  feet  of 
height.  Previous  to  that  event  it  was  the  loftiest  volcano  in  Java,  having  an 
altitude  of  9000  feet.  At  the  time  of  the  eruption  it  was  thought  that  this 
great  cone  had  been  engulfed  and  a  vast  area  of  land,  amounting  to  go  square 
miles,  swallowed  up,  including  40  villages.  Later  investigations  have  shown 
that  the  top  of  the  cone  was  undoubtedly  destroyed  by  an  explosion,  not  dis- 
similar to  that  of  Krakatoa.  and  that  the  villages  were  buried  beneath  the  vast 
mass  of  dust,  sand,  and  scoria  blown  from  the  summit. 

In  1815,  Tomboro.  on  the  island  of  Sumbawa,  200  miles  from  Java,  burst 
forth  with  such  violence  that  the  explosions  were  heard  at  the  distance  of  970 
miles. 

Causes  of  Volcanic  Action.  —  The  fundamental  cause  of  vol- 
canic action  is  undoubtedly  the  expansive  force  of  compressed 
steam  and  other  gases.  Two  cases  are  conceivable  :  The  com- 
pressed steam  and  gases  may  be  free,  that  is,  not  blended  with 
the  lava ;  or  they*  may  be  imprisoned  within  the  substance  of 
the  lava.  The  force  developed  will  be  the  same  in  either  case, 
but  the  mode  of  action  will  be  different. 

I.  The  actioti  of  free  gases. —  We  have  already  seen  that  at 
a  comparatively  shallow  depth  the  earth  is  intensely  hot  and 
that  water  readily  finds  its  way  through  crevices  in  rocks  or  be- 
tween the  strata.  Should  this  water,  or  a  portion  of  it,  come  in 
contact  with  heated  matter,  the  effect  will  be  to  convert  it  into 
steam.  This  may  be  done  with  great  suddenness.  Then  con- 
ditions would  arise  such  as  cause  the  explosion  of  steam  boilers. 

A  careless  engineer  allows  the  water  in  his  boiler  to  get  low,  but  still  keeps 
up  the  fire.  Into  the  intensely  heated  boiler  he  admits  water,  which  is  now 
converted  into  steam  with  such  rapidity  and  in  such  quantity  that  it  cannot 
possibly  escape.  The  boiler  is  unable  to  resist  the  pressure,  and  an  explosion 
takes  place. 

Water  that  finds  its  way  into  the  heated  subterranean  regions 
of  the  earth  may  be  suddenly  converted  into  steam.     The  re- 


CAUSES   OF   VOLCANIC    ACTION  59 

suit  is  an  eruption  of  the  explosive  type  and  the  liberation  of 
vast  quantities  of  water  vapor,  dust,  sand,  and  other  fragmentary 
products. 

2.  The  action  of  absorbed  gases.  —  The  second  case,  in  all 
probability,  occurs  more  commonly  than  the  first,  and,  in  fact, 
seems  to  offer  a  possible  explanation  for  most  of  the  phenom- 
ena of  a  volcanic  eruption. 

A  number  of  substances,  solid  and  liquid,  absorb,  under  pres- 
sure and  at  high  temperatures,  steam  and  other  gases.  Lava  is 
one  of  these.  If  thus  charged  the  lava  in  a  volcanic  conduit 
should  be  relieved  of  pressure  by  the  overflow  at  the  vent,  its 
capacity  for  retaining  the  gases  in  absorption  would  be  dimin- 
ished. They  would  expand  and  force  the  lava  in  whatever  may 
be  the  direction  of  least  resistance  precisely  as  the  volume  of 
gases  liberated  from  gunpowder  and  similar  substances  expands 
and  forces  obstacles  before  it  with  explosive  violence. 

Among  other  things  this  satisfactorily  explains  the  pulveriza- 
tion of  lava  and  the  production  of  volcanic  sand  and  ashes. 
The  gases  absorbed  by  the  lava  being  relieved  from  pressure 
blow  it  into  powder,  as  wood  is  blown  to  pulp  for  making 
paper. 

Some  writers  consider  that  volcanoes  are  due  to  the  shrinkage  of  the  crust 
of  the  earth  compressing  and  forcing  upward  molten  matter  from  subterranean 
regions. 

It  has  also  been  suggested  that  the  extrusion  of  the  lighter  lavas  may  be 
due  to  the  sinking  of  the  more  condensed  or  heavier  rock  above  under  the 
influence  of  gravity.  This  would  explain  the  quiet  welling  out  of  lava  in  some 
volcanic  eruptions,  especially  fissure  eruptions.  Steam,  however,  is  admitted 
to  be  the  only  agency  which  accounts  for  the  explosive  character  of  eruptions. 


STATE  HOKMALSCi 


IlOS  AI^CEUES,  CHIt. 


VII.    EARTHQUAKES 

An  Earthquake  is  the  shaking  or  trembling  of  the  crust  of  the 
earth  due  to  the  transmission  of  a  jar,  shock,  or  impulse  —  in  the 
form  of  earth  waves  —  which  has  its  origin  below  the  surface. 
It  may  be  nothing  more  than  a  slight  tremor  similar  to  that  pro- 
duced by  the  passage  of  a  heavily  loaded  wagon  along  the 
street,  or  it  may  be  a  movement  of  such  violence  as  to  over- 
throw and  destroy  whole  cities. 

Earthquakes  are  usually  preceded  by  a  rumbling  noise,  like 
distant  thunder,  then  the  ground  rises  and  falls,  houses  rock  to 
and  fro  until  they  are  rent  from  top  to  bottom  or  fall  with  a  crash 
into  ruins.  In  some  cases  the  earth  opens  with  gaping  cracks 
which  either  close  again  or  are  permanent.  In  a  few  seconds  a 
city  may  be  demolished  and  hundreds  of  its  inhabitants  dead  or 
dying. 

Earth  waves,  like  sound  waves,  are  elastic  waves.  From  their 
origin,  known  as  the  caitnim  or  focus,  they  spread  through  the 
crust  in  all  directions.  Although  usually  regarded  as  a  point, 
the  focus  is  probably,  in  most  instances,  -a.  fissure  of  displacement 
ox  fault.  Its  depth  below  the  surface  is  beheved  rarely  to 
exceed  lo  or  15  miles,  and  oftentimes  it  may  be  less. 

If  the  materials  of  the  crust  were  of  the  same  composition, 
temperature,  and  density  throughout,  earth  waves  would  pass 
outward  from  the  focus  in  spherical  shells  of  alternate  compres- 
sion and  rarefaction,  and  the  surface  zvaves,  or  visible  waves, 
would  be  the  outcroppings  of  spherical  waves  which  spread  in 
circles  from  a  point  directly  over  the  centrum,  known  as  the 
epiccntrum,  as  shown  in  the  accompanying  diagram. 

There  is,  however,  reason  for  believing  that  earth  waves  are 
ellipsoidal  rather  than  spherical,  on  account  of  their  accelerated 

60 


DURATION   OF   EARTHQUAKES  6 1 

velocity  in  the  deeper  and  more  elastic  portions  of  the  earth's 
crust,  and,  further,  that  the  centrum  occupies  one  focus  of  the 
ellipsoid. 

Owing  to  the  different  materials  encountered  and  the  vary- 
ing conditions  affecting  elasticity,  an  earthquake  must  be  re- 
garded as  a  very  complicated   earth   movement  in  which   the 


C 

Diagram  illustrating  the  Propagation  of  Earth  Waves 

C,  the  focus  or  centrum  ;  B,  the  epicentrum  or  point  on  the  surface  where  the  shock  is  verti- 
cal ;  A,  point  on  the  surface  where  the  shock  may  be  destructive,  as  here  the  oscillation 
contains  two  elements,  the  horizontal  as  well  as  the  vertical.  It  should  be  noted  that, 
if  the  crust  block  is  homogeneous  throughout,  the  surface  waves,  which  are  the  out- 
cropping spherical  waves,  spread  in  ever  increasing  circles  from  the  point  B. 

waves  are  subject  to  many  and  intricate  deviations  from  their 
theoretical  shape,  whether  spherical  or  ellipsoidal. 

The  velocity  of  earth  waves  varies,  depending  upon  the  in- 
tensity of  the  shock,  the  nature  of  the  media  through  which 
they  pass,  and  the  distance  from  the  centrum,  or  point  of  origin. 

The  wave  velocity  of  the  well-known  Charleston  earthquake  of  August, 
1886,  was  found  to  be  about  190  miles  per  minute:  that  of  the  Japanese 
earthquake  of  October,  1891.  about  78  miles  per  minute.  Although  the  speed 
of  earth  waves  is  quite  rapid,  it  varies  through  a  very  wide  range. 

Duration  of  Earthquakes.  —  Earthquakes  may  be  momentary, 
or  they  may  consist  of  several  successive  shocks,  and  these  may 
be  repeated  during  long  periods.  After  the  earthquake  which 
in  1766  destroyed  a  large  portion  of  the  city  of  Cumana  in  Vene- 
zuela, shocks  were  felt  nearly  every  hour  for  14  months;  and 


62  EARTHQUAKES 

ill  Calabria,  southern  Italy,  beginning  with  the  earthquake  of 
February,  1783,  they  were  felt  for  nearly  four  years. 

In  Saint  Thomas,  also,  after  the  earthquake  of  1867,  and  at 


Diagram  illustrating  the  Ellipsoidal  Shape  of  Earth  Waves 

C,  the  centrum  in  one  focus  of  the  ellipsoid;  B,  the  epicentrum.  In  the  passage  of  the 
waves  from  the  centrum  to  the  epicentrum  they  would  constantly  encounter  less  cohe- 
rent matter  and  their  velocity  would  be  diminished.  This  is  shown  by  decreasing  the 
distance  between  the  waves.  In  the  opposite  direction,  for  reasons  stated  in  the  text, 
their  velocity  would  be  accelerated.  This  is  shown  by  increasing  the  distance  between 
the  waves.  Likewise  in  other  directions  the  passage  of  the  waves  would  be  affected 
more  or  less  according  to  the  depth  below  the  surface,  thus  producing  the  ellipsoidal 
shape. 


Charleston  after  that  of  1886,  minor  shocks  were  felt  for  many 
weeks. 

Area  of  Disturbance.  —  The  area  through  which  the  disturb- 
ance extends  may  be  very  large.  The  shock  of  the  earthquake 
of  Lisbon,  in  1755,  was  definitely  felt  as  far  as  Finland  in 
one  direction,  and  as  far  as  Madeira  in  another. 

The  disturbance  affected  the  sea  to  a  much  greater  distance. 
The    water    rose    among    the    West    Indies    so    that  Antigua, 


GREAT   SEA-WAVES 


63 


Martinique,  Guadeloupe,  and  Barbados  were  partly  overflowed. 
The  area  disturbed  was  four  times  as  large  as  Europe. 

The  Charleston  earthquake  was  the  most  severe  ever  experi- 
enced in  the  eastern  part  of  the  United  States.  Shocks  were 
felt  from  New  England  to  Florida  and  from  the  Atlantic  coast 
to" the  middle  of  the  Mississippi  Valley.     It  has  been  estimated 


Wreck  of  a  Business  Block,  California  Earthquake  of  1906 


that  the  area  of  disturbance  embraced  fully  one  fourth  of  the 
entire  country,  shocks  having  been  felt  in  no  less  than  28 
states. 

Great  Sea  Waves  are  caused  by  earthquakes  which  have  their 
center  beneath  the  ocean  bed. 

The  water  at  first  recedes  from  the  beach,  and  exposes  the 
sea  bottom  even  beyond  the  usual  limits  of  low  water.  Then 
the  sea  wave  comes  in  with  a  steep  front  or  wall  which  may  be 
50  or  60  feet  high.      It    drives   back  the    receding  water,  and 


64  EARTHQUAKES 

deluges  the  shore,  sometimes  demolishing  whole  towns.  It 
often  passes  inland  to  the  distance  of  several  miles.  The  in- 
habitants, when  possible,  rush  to  the  hills,  and  remain  there  until 
the  wave  subsides.  In  many  instances  the  loss  of  life  has  been 
appalHng. 

The  great  wave  of  the  Lisbon  earthquake  was  60  feet  high  at  Cadiz.  It 
rose  and  fell  18  times  at  Tangier,  Africa. 

In  1854,  when  Simoda,  in  Japan,  was  destroyed  by  an  earthquake,  the  sea 
wave  completely  overwhelmed  the  place.  The  receding  wave  actually  crossed 
the  Pacific,  and  made  the  water  rise  on  the  coast  of  California. 

Agam,  in  June,  1896,  during  an  earthquake  having  its  center  beneath  the 
Pacific  off  the  northeastern  coast  of  Hondo,  Japan,  the  shore  of  that  island 
for  the  distance  of  70  miles  was  washed  by  a  great  sea  wave.  Many  vil- 
lages and  towns  were  destroyed  and  upward  of  30,000  people  perished.  The 
magnitude  of  the  sea  disturbance  is  shown  by  the  fact  that  at  Honolulu,  3591 
miles  away,  waves  attained  a  height  of  eight  feet  above  high  water.  As  in  the 
preceding  case,  the  disturbance  was  registered  by  proper  instruments  on  the 
coast  of  California. 

The  earthquake  at  Arica,  Peru,  in  August,  1868,  was  likewise  remarkable 
on  account  of  the  size  of  the  accompanying  sea  waves.  Owing  to  the  fact 
that  the  waves  travel  faster  through  the  land  than  through  the  water,  to  the 
ruin  wrought  by  earth  shocks  was  added  the  destruction  caused  by  the  inun- 
dation of  the  sea. 

After  the  passage  of  the  first  earth  waves  the  water  receded  from  the 
shore,  then  it  rose  to  the  height  of  30  feet  and  overflowed  the  town.  Again 
the  water  receded,  and  again  it  rose  in  a  great  wave.  Then  came  terrific 
shocks  followed  by  the  advance  inland  of  a  perpendicular  wall  of  water,  from 
42  to  45  feet  in  height,  capped  with  foam.  It  rushed  over  the  land,  carrying 
with  it  several  ships,  among  them  two  naval  vessels,  which  were  left  stranded 
far  from  the  shore. 

Sea  waves  are  often  perceptible  throughout  an  entire  ocean  basin.  They 
travel  across  the  Pacific  at  the  rate  of  about  350  miles  an  hour. 

If  the  center  of  the  earthquake  is  beneath  the  land,  so  near  the  coast  as  to 
disturb  the  sea,  the  waves  produced  are  thrown  out  from  the  shore  and  are 
harmless.  This  explains  why,  although  the  Charleston  earthquake  was  felt 
at  sea  as  far  as  the  Bermudas,  no  wave  damage  was  done  in  the  harbor  of 
Charleston. 

Destructive  Effects.  —  Earthquakes  are  perhaps  the  most  im- 
pressive manifestations  of  power  in  the  material  world.  The 
destruction  of    life  and  property  occasioned  by  them  is  often 


UPHEAVALS   AND   DEPRESSIONS  65 

enormous.  On  the  ist  of  November,  1755,  "Lisbon  was  shaken 
by  the  "  great  earthquake,"  and  in  six  minutes  its  palaces  were 
in  ruins  and  60,000  of  its  inhabitants  were  dead. 

In  March,  18 12,  Caracas,  in  Venezuela,  was  destroyed,  with 
10,000  of  its  inhabitants. 

Upheavals  and  Depressions.  —  Geological  changes  of  great 
importance  often  accompany  earthquakes. 

In  the  year  18 19  an  earthquake  occurred  in  the  region  ad- 
jacent to  the  mouth  of  the  Indus.  It  completely  destroyed  the 
town  of  Bhooj,  and  was  felt  within  a  radius  of  hundreds  of 
miles.  A  tract  to  which  the  natives  gave  the  name  of  "Allah 
Bund,"  or  "  Mound  of  God,"  was  raised  where,  before,  there 
had  been  a  level  plain.  The  "  Bund "  was  50  miles  long, 
16  miles  wide,  and  about  10  feet  high.  At  the  same  time 
the  fort  and  village  of  Sindree,  with  the  neighboring  region, 
subsided  ;  the  sea  flowed  into  the  sunk  area,  and  an  inland  sea 
was  formed  covering  2000  square  miles. 

During  the  earthquake  at  New  Madrid,  on  the  Mississippi, 
in  181 1-1812,  which  covered  a  period  of  several  months,  an  area, 
75  or  80  by  30  miles  in  size,  lying  west  of  the  town  and  since 
known  as  the  "sunk  country,"  was  permanently  submerged. 

Distribution  of  Earthquakes.  — No  part  of  the  earth  is  entirely 
free  from  earthquakes.  In  certain  parts  of  Japan  tremors 
are  felt  every  day.  Vessels  not  unfrequently  report  earthquake 
shocks  at  sea. 

In  the  Old  World  they  are  most  frequent  in  a  region  which 
embraces  the  northern  shores  of  the  Mediterranean  Sea,  and  ex- 
tends eastward  into  the  central  portions  of  Asia. 

In  the  New  World  earthquakes  are  far  more  common  than  in 
the  Old.  Both  the  eastern  and  western  mountain  regions  of 
North  America  are  subject  to  them,  but  the  region  of  greatest 
frequency  is  in  South  America.  It  comprises  Ecuador,  Peru, 
and  Chile. 

In  many  places  within  this  region  the  houses  are  built  of  reeds  and  bamboo, 
lashed  by  thongs  of  bull's  hide,  and  secured  in  their  places  with  cords  instead 
of  nails,  that  they  may  yield  to  the  shocks  without  being  shaken  to  pieces. 


66 


EARTHQUAKES 


Causes  of  Earthquakes.  —  Earthquakes  have  been  attributed 
to  various  causes,  such  as  displacements  of  the  earth's  crust, 
slumping,  volcanic  action,  and  the  collapse  of  caverns. 

(i)  Geologists  are  of  the  opinion  that  in  most  instances  an 
earthquake  is  due  to  the  formation  of  a  fissure  in  the  crust,  and 
that,  in  the  process  of  readjustment  following,  one  wall  slips  or 


Diagram  illustrating  Faulting  of  the  Earth's  Crust 

a,  a,  b,  fault  fissure. 

slides  over  the  other  with  sufficient  violence  to  produce  a  series 
of  jolts  or  jars.  These,  transmitted  through  the  adjoining  rocks, 
constitute  an  earthquake.  The  displacement  is  known  as  a  fault ; 
earthquakes,  therefore,  may  result  from  \.\\q  faulting  of  the  crust. 

Faulted  rocks  are  illustrated  in  the  accompanying  figure.  By  the  forma- 
tion of  the  fissure  aab  and  the  resulting  displacement,  the  strata  on  the 
right,  or  downthrow  side,  have  dropped  to  a  lower  level. 

The  great  California  earthquake  of.  April  i8,  1906.  the  severest  known  on 
the  Pacific  coast  of  the  United  States,  was  undoubtedly  caused  by  the  shifting 
and  readjustment  of  the  rocks  along  an  old  line  of  weakness  or  faulting  ex- 
tending from  Bolinas  Bay,  north  of  the  Golden  Gate,  over  the  peninsula  of 
San  Francisco  to  Salinas  and  perhaps  farther  south. 

While  the  damage  resulting  from  earth  movements  was  very  great  both  in 
San  Francisco  and  the  neighboring  towns,  to  the  calamity  in  San  Francisco 
was  added  the  tremendous  loss  of  property  by  fire,  which,  following  the 
collapse  of  buildings,  swept  over  the  entire  business  portion  of  the  city. 


CAISKS    OK    1:ART1I(H  AKKS 


67 


But  if  earthquakes  are  produced  by  faulting,  how  is  that 
phenomenon  to  be  explained  ?  It  is  now  believed  to  be  one  of 
the  results  of  the  cooling  and  contraction  of  the  interior  of  the 
earth.     As  the  inner  rocks  cool  and  contract,  they  shrink  away 


Fissure  of  Displacement,  Japan  EAKiiini  ake  oi-  1891 

from  the  outer  layers,  some  portions  of  which  are  left  without 
support.  Under  the  pressure  of  gravity  they  may  now  bend  or 
they  may  break.  Having  broken,  they  may  slide  and  grind  on 
the  lower  wall  of  the-fissure.  The  effect  upon  the  senses  may 
be  faintly  illustrated  by  the  jarring  and  noise  produced  by  a 
heavy  body  of  snow  when  it  slides  from  the  roof  of  a  large 
church. 

By  reference  to  page  86  it  will  he  seen  that  the  ahove  cause  furnishes  the  best 
explanation  yet  oftered  not  only  fur  the  formation  of  fault?  and  fissures,  but 
also  for  the  formation  of  the  great  mountain  systems  of  the  earth.;  vvl)ether-  of 
the  folded  or  block  type.  If. this  view  be  correct,  then,  when  mountain  mak- 
ing is  going  on.  earthquakes'  should  be  of  common    occurrence.     -We- 4iave 

M.-S.  PHYS.  GK.O(;.  —  5 


68 


EARTHQUAKES 


reason  to  believe  that  such  was  the  case  in  the  past,  as  it  undoubtedly  is  in  the 
present. 

(2)  There  are  earthquakes  which  seem  to  arise  from  volcanic 
action,  especially  that  of  the  explosive  type,  but  tremors  of  this 
kind  affect  a  much  smaller  area  than  the  preceding.     As  to  their 

cause,  it  has  been 
suggested  that  the 
sudden  formation  and 
explosion  of  steam 
within  a  cavity  of  the 
earth  or  its  rapid  con- 
densation  accom- 
panied by  a  collapse 
might  account  for  the 
phenomena,  or,  in 
other  cases,  the  pene- 
tration of  the  rocks 
by  molten  lava. 

Earthquakes  are  of  com- 
mon occurrence  in  the 
vicinity  of  the  Mediter- 
ranean volcanoes,  Vesu- 
vius, Etna,  and  Stromboli. 
An  earthquake  of  un- 
usual severity  occurred  on 
the  slope  of  Mauna  Loa, 
a  Hawaiian  volcano,  in  the 
spring  of  1868.  For  six 
days  shock  followed  shock 
with  increasing  violence. 
"  The  ground  rolled  in 
great  wa\es,  rapidly  sway- 
ing in  every  conceivable 
direction,  including  the 
Displacement  of  Railroad  Track  by  Earth-  vertical."  The  crests  of 
QUAKE  Fault  or  Rift.  Two  Views  of  the  ^^e  earth  waves  cracked 
Track  of  the  North  Shore  Railroad  at  open ;  finally  a  sheet  of 
ToMALES,  Marin  County,  California,  after  molten  lava  was  projected 
THE  Earthquake  of  1906  violentlv  skvward. 


CAUSES   OF   EARTHQUAKES 


69 


(3)  In  some  instances  earthquakes  of  a  local  character  have 
been  attributed  to  the  collapse  of  caverns.  In  limestone  regions 
especially,  throusjh  the  dissolving  action  of  subterranean  water, 


Fault   Line  at  Olema,  Marin  Countv,  California.     Typical   Appearance 
IN  Hard  Ground.    Earthquake  of  1906 

large  caves  are  formed.  As  they  are  enlarged  their  roofs  are 
weakened  and  in  places  may  finally  fall.  The  jar  thus  produced 
may  be  sufficient  to  account  for  a  small  earthquake. 

The  collapse  of  Mount  Cernans  in  1840  has  been  cited  as  an  example  of  the 
probable  action  of  underground  water.  The  Jura  Mountains  are  especially 
noted  for  their  large  springs.  In  this  particular  instance  many  years  before  a 
large  spring  had  disappeared  which  thereafter,  by  dissolving  the  underlying 
rock,  may  have  made  possible  the  fall  of  the  mountain.  Earthquakes  from 
such  a  cause  are  not  common. 


PART    IL  — THE   LAND 


VIII.    THE    LAND    MASSES 

Relation  of  Land,  Water,  and  Air. — In  the  preceding  pages 
we  have  regarded  the  earth  as  a  whole.  In  those  which  are  to 
follow  we  shall  consider  somewhat  in  detail  those  parts  of  the 
earth  which  are  accessible  to  man —  the  solid  portion  or  litJio- 
spheir,  the  watery  portion  or  hydrosphere,  and  the  aerial  portion 
or  atmosphere ;  we  shall  also  consider  the  phenomena  which 
belong  to  each  and  the  forms  of  life  which  they  support. 

Although  easily  recognized  and  apparently  distinct,  the  litho- 
sphere,  hydrosphere,  and  atmosphere  interpenetrate  one  another 
in  a  most  remarkable  manner,  and  this  interpenetration  has  a 
most  important  bearing  upon  life.  Were  it  not  for  air  in  the 
water,  fish  would  perish  ;  were  it  not  for  water  in  the  ground, 
most  plants  would  die  and  animals  starve  ;  were  it  not  for  water 
in  the  atmosphere,  rainfall  would  cease  and  desolation  reign. 
Further  illustrations  are  unnecessary  to  show  that  the  land,  the 
water,  and  the  air  are  to  be  regarded  as  parts  of  a  great  mechan- 
ism which  contributes  in  a  variety  of  ways  to  the  maintenance 
of  plant  and  animal  life. 

Distribution  of  Land.  —  Of  nearly  197,000,000  square  miles 
which  embrace  the  surface  of  the  earth,  about  142,000,000  are 
covered  by  water,  and  55,000,000  by  land.  In  other  words, 
there  is  over  two  and  one  half  times  as  much  water  as  land. 

The  land  is  found  in  masses  of  irregular  shape  and  size,  which 
are  separated  by  intervening  portions  of  water.  The  three 
largest  continuous  land  masses  are  called  continents.  The 
smaller  masses  of  land  are  called  islands. 

Most  of  the   land   is  in  the  northern   half  of   the  globe.      It 

70 


NORlllKKN    AND    SOL:  II IKRN    HKMISI'HKKKS  J  \ 

surrounds  the  North  Pole  in  an  almost  continuous  ring,  and 
from  the  polar  regions  it  extends  in  long  irregular  masses 
toward  the  south.  We  may  consider  the  great  land  masses  as 
forming  three  pairs  of  grand  divisions.  The  pair  comprising 
North  America  and  South  America  affords  the  most  perfect 
example  of  this  arrangement  ;  that  consisting  of  Europe  and 
Africa  is  less  well  defined  ;  while  that  is  most  irregular  which 
comprises  Asia  and  Australia. 

In  regard  to  shape  the  grand  divisions  follow  a  general  law. 
They  spread  out  broadly  toward  the  north,  while  toward  the 
south  they  taper  to  points,  or  throw  out  peninsulas.  Thus,  in 
general,  they  approach  the  form  of  a  triangle.  This  is  strik- 
ingly illustrated  in  the  case  of  Africa  and  the  two  Americas. 
Europe  and  Asia  combined  form  a  vast  triangle.  Australia  is 
the  only  marked  exception  to  the  rule. 

Almost  all  the  large  peninsulas  are  southern  projections  from 
the  grand  divisions. 

Northern  and  Southern  Hemispheres. — The  globe  is  divided 
by  the  equator  into  a  Northern  and  Southern  Hemisphere. 
North  America,  Europe,  and  Asia,  two  thirds  of  Africa,  and 
a  portion  of  South  America  are  contained  in  the  Northern  ; 
Australia,  part  of  Africa,  and  the  greater  part  of  South  America, 
in  the  Southern.  There  is  three  times  as  much  land  in  the 
Northern  as  in  the  Southern  Hemisphere. 

The  Northern  Hemisphere  is  the  seat  of  knowledge,  civiliza- 
tion, and  power.     It  is  the  commercial  hemisphere. 

The  Southern  Hemisphere  has  never  been  the  seat  of  power. 
The  Peruvians  and  the  Javanese  were  the  only  nations  which 
attained  a  high  degree  of  civilization  there.  Only  about  one 
fifteenth  of  the  population  of  the  globe  have  their  home  within 
this  hemisphere. 

Land  and  Water  Hemispheres.  —  The  earth  may  be  divided 
into  two  hemispheres,  one  of  which  contains  nearly  all  the 
land,  and  the  other  nearly  all  the  water.  These  hemispheres 
are  known  as  the  Land  Hemisphere  and  the  Water  Hemi- 
sphere.     London  is  nearly  at  the  center  of    the    Land   Hemi- 


72 


THE   LAND    MASSES 


sphere;  New  Zealand  nearly  at  that  of  the  Water  Hemisphere. 
Australia  presents  the  largest  extent  of  land  in  the  Water 
Hemisphere. 

Coast  Line  of  the  Grand  Divisions.  —  Everywhere  the  sea  more 
or  less  deeply  indents  the  land.  These  indentations  form  navi- 
gable seas  or  sounds,  harbors  or  roadsteads.     The  length  and 


The  Land  Hemisphere 

indentation  of  the  coast  line,  therefore,  are  indications  of  the 
commercial  capabilities  of  a  grand  division. 

Comparing  the  several  grand  divisions,  we  find  that  the 
southern  have  far  more  regular  outlines  than  the  northern. 
Their  indentations  are  comparatively  limited,  and  their  coast 
line  short.  The  contrast  is  most  marked  between  Europe  and 
Africa. 


COAST   LINE   Ot-"   THE   GRAND    DIVISIONS  73 

Europe  has  six  times  more  coast  line  in  proportion  to  its  area 
than  Africa.  The  effect  of  this  has  been  very  important  in  the 
history  of  the  two  grand  divisions.  By  the  multitudinous  seas, 
bays,  and  gulfs  of  Europe  intercommunication  of  one  part  of  the 
grand  division  with  another,  and  with  other  portions  of  the  world, 
has  been  facilitated,  and  thus  its  several  countries  have  been 


The  Water  Hemisphere 


rendered  accessible  to  commerce  and  civilization,  Europe  has 
enjoyed  among  the  grand  divisions  the  leadership  in  commerce. 

Africa,  on  the  other  hand,  with  its  comparatively  unbroken 
coast  line  and  scanty  harbors,  has  been  rendered  by  nature  far 
less  open  to  extensive  intercourse  with  the  outside  world. 

North  America,  though  in  a  less  degree  than  Europe,  is 
preeminent  for   the   indentation  of    its    sea   coast.     This    con- 


74  THE   LAND    MASSES 

tributes    to  render  it  the  companion  of    Europe  in    commerce 
and  civilization. 

Coast  Lines  not  Permanent.  —  In  past  ages  of  the  earth  much 
that  is  now  land  was  accumulated  beneath  the  sea  in  the  form 
of  silt,  sand,  and  limy  deposits.  From  time  to  time  these 
deposits  were  elevated  above  the  water,  forming  new  land. 
Thus  coast  lines  were  changed  and  the  shape  of  the  land 
masses  altered.  But  this  was  not  all.  There  were  movements 
of  depression  as  well  as  elevation.  By  the  sinking  of  the  land 
rivers  were  drowned  and  estuaries  formed,  and  by  the  subsidence 
of  coastal  mountains,  islands  were  left  as  offshore  monuments 
of  a  retreating  coast.  These  are  some  of  the  results  arising 
from  diastropJiic  or  great  earth  movements.  Even  during  the 
present  time  in  many  places  the  land  has  given  way  before 
the  incessant  beating  of  the  waves,  while  in  other  places  the 
shore  has  been  extended  by  the  formation  of  sand  reefs  and 
mud  fiats.  So  it  must  have  be^^n  in  the  past.  The  coast  lines, 
therefore,  are  not  permanent  and  the  shape  of  the  continents 
has  undergone  many  alterations.  There  has  been,  however,  an 
upbuilding  or  evolution  of  the  land  from  the  primitive  nuclei  to 
the  more  highly  developed  areas  which  now  furnish  an  abiding 
place  for  man.  Yet,  notwithstanding  these  changes,  broadly 
speaking,  both  the  land  masses  and  the  oceanic  basins  exhibit 
a  high  degree  of  permanency. 


IX.     RELIEF   OF   THE   LAND 

General  Statement.  —  The  relief  of  the  land  is  shown  by  its 
"  physical  features,"  or  the  irregularities  of  its  surface,  such  as 
plains,  hills,  plateaus,  mountains,  and  valleys.  Although  differ- 
ing greatly  in  form,  they  represent,  in  the  main,  the  combined 
results  of  two  opposing  forces:  earth  movements  and  erosion. 

By  earth  movements  reference  is  ma'de  not  only  to  the 
great  upheavals  by  which  the  continents  were  elevated,  but  also 
to  the  yielding  of  the  earth's  crust,  through  folding  and  faulting, 
in  the  formation  of  mountains.  By  erosion  is  meant  the  wast- 
ing or  degrading  of  the  land,  chiefly  by  the  action  of  water, 
whether  in  the  liquid  or  the  solid  state.  By  this  action  all 
elevations  are  more  or  less  modified,  and  in  the  past  plateaus 
and  even  mountains  have  been  reduced  to  the  condition  of  low 
plains. 

Relief,  therefore,  cannot  be  regarded  as  permanent.  The 
forces  concerned  may  act  with  great  slowness  ;  but  time  is  long, 
and  although  the  changes  wrought  are  apparently  insignificant, 
their  ultimate  result  may  be  to  change  completely  the  physical 
aspect  of  the  land. 

Mean  Height  of  the  Land.  —  The  average  elevation  of  the  con- 
tinents is  not  great.  It  has  been  estimated  that  if  all  the  moun- 
tains were  leveled,  and  all  the  valleys  filled  up,  the  land  of  the 
globe,  taken  as  a  whole,  would  not  be  raised,  on  an  average, 
much  over  2400  feet  above  the  sea. 

Although  the  mountains  are  so  massive  in  size,  and  reach  so  far  toward 
the  heavens  that  their  hio^hest  peaks  can  with  the  greatest  difficulty  be  scaled, 
yet,  when  compared  with  the  size  of  the  earth,  their  huge  proportions  dwindle 
into  insignificance. 

X  mountain  five  miles  high,  which  is  higher  than  any  but  the  loftiest  peaks 
of  the  Himalaya  or  Karakoram,  rises  above  the  sea  level  but  gjy  part  of  the 

75 


76  RELIEF   OF  THE   LAND 

earth's  radius.  Hence  upon  a  globe  i6  inches  in  diameter,  it  would  be 
represented  by  an  elevation  of  only  j^-g  of  an  inch,  about  the  thickness  of 
three  leaves  of  this  book. 

On  a  globe  i6  feet  in  diameter,  the  highest  mountains  would  rise  above 
the  surface  less  than  one  eighth  of  an  inch. 

Forms  of  Relief.  —  According  to  their  relief,  the  various  forms 
of  land  are  classified  as  lowlands  or  highlands. 

Lowlands  are  usually  elevated  less  than  looo  feet  above  the 
sea.     They  are  commonly  called  plains. 

Highlands  have  an  elevation  of  looo  feet  or  more  above  the 
sea.  They  are  called  plateaus  or  table-lands  and  mountains. 
Hills  are  inferior  elevations.  They  may  rise  from  plains  or 
from  plateaus ;  they  may  fringe  a  table-land  from  which  they 
have  been  separated  by  erosion ;  or  they  may  be  piled  one 
above  another  at  the  base  of  mountains.  In  the  condition 
last  mentioned  they  are  termed  footJiills. 

Between  the  various  forms  of  relief  sharp  distinctions  cannot  always  be 
drawn.  Plains,  for  example,  may  gradually  pass  into  plateaus,  and  hills  may 
so  closely  resemble  mountains  as  to  be  with  difficulty  separated  from  them. 

Plains  are  those  portions  of  the  earth's  surface  which  have 
only  a  moderate  elevation  above  the  sea.  They  may  be  level, 
rolling,  or  diversified  with  hills.  When  covered  with  grass  and 
generally  destitute  of  trees,  they  are  called  prairies  in  our  coun- 
try, pampas  or  llanos  in  South  America,  and  steppes  in  Asia. 
The  densely  wooded  plains  of  the  Amazon  are  called  silvas. 
About  one  half  of  the  continental  surfaces  consists  of  plains. 

For  convenience  plains  may  be  grouped  as  follows :  coastal 
plains,  river  and  lake  plains,  and  interior  plains.  It  must  be 
understood,  however,  that  these  groups  are  not  always  distinct, 
for  one  form  may  imperceptibly  blend  with  another,  as  is  con- 
spicuously shown  in  the  case  of  the  Gulf  coastal  plain  and  the 
flood  plain  of  the  Mississippi  River  in  several  of  the  Southern 
states. 

Coastal  Plains,  as  their  name  implies,  are  those  bordering 
coasts.  They  have  been  formed  beneath  the  sea  and  later 
elevated  into  land.    Of  this  there  can  be  no  doubt.     The  loosely 


COASTAL   PI^INS 


77 


compacted  strata  of  sand  and  gravel,  the  beds  of  silt  and  clay, 
the  presence  of  sea  shells  and  the  hard  parts  of  other  marine 
animals  furnish  indisputable  evidence.  Such  plains,  lying  be- 
tween the  highlands  and  the  shore,  are  in  some  instances  quite 
broad,  as  along  the  Atlantic  coast  of  the  United  States  from 
New  Jersey  southward ;    in  other  instances  they  are  narrow, 


A  Narrow  Coastal  Plain 

sometimes  quite  narrow,  as  shown  by  the  low-lying  strips  frin- 
ging, in  many  places,  the  Pacific  coast  of  both  North  and  South 
America. 

The  beds  or  strata  underlying  a  coastal  plain  incline  or  dip 
seaward  at  a  low  angle.  They  are  also  of  varying  degrees  of 
hardness.  As  soon  as  the  newly  made  plain  emerges  from  the 
sea  a  stripping  of  its  surface  begins.  The  chief  agents  con- 
cerned in  this  are  rain,  running  water,  and  ice,  and  the  process 
as  a  whole  is  termed  denudation.  Streams  from  the  higher 
land  now  pass  down  over  the  plain,  excavating  shallow  chan- 
nels. As  the  plain  rises  higher,  the  stream  ways  are  deepened 
and  tributary  streams  may  originate  upon  its  surface.  The 
softer  the  rocks,  the  more  rapid  the  denudation  becomes.     If  in 


78 


RELIEF   OF   THE    LAND 


time  it  should  happen  that  where  the  softer  strata  outcrop  the 
plain  is  trenched  and  where  the  hard  strata  outcrop  there  is 
left  a  belt  of  upland,  presenting  a  scarp  to  the  interior  and  a 


A  Belted  Coastal  Plain 
The  strata  are  inclined  (dip)  seaward.    At  the  base  of  the  upland  the  plain  is  trenched. 
Here  the  weaker  strata  have  yielded  to  erosion,  while  the  harder  strata  above  form  an 
inward-facing  scarp. 

seaward  slope  to  the  exterior,  on   account  of  its  belted  relief 
such  a  plain  would  be  termed  a  belted  plain. 

The  conditions  above  described  appear  in  southern  New  Jersey.  Here  the 
Delaware  River  in  its  lower  course  flows  in  the  trenched  portion  of  the  coastal 
plain.  To  the  southeast  the  land  becomes  hilly  and  passes  into  an  upland 
belt  which  on  its  seaward  side  slopes  gradually  to  the  lowland  skirting  the 
shore. 

River  and  Lake  Plains  are  often  termed  alluvial  plains.  They 
have  been  formed  from  materials  washed  down  from  hills  and 
mountains.  In  the  lower  course  of  a  river,  where  the  amount 
of  sediment  received  is  greater  than  the  current  can  urge  on- 
ward, the  inequalities  of  the  river  bed  are  buried  beneath  alluvial 
deposits  which  form  a  bottom  land  subject  to  overflow  in  times 
of  flood.  Such  an  area  is  known  as  a^<w<^//'/rt'/;/.  An  extension 
of  a  flood  plain  into  a  lake  or  sea  may  take  place,  and  if  the 
stream  is  impeded  by  the  accumulated  matter,  it  may  discharge 


KIVKK    AM)    I.AKK    PLAINS 


79 


through  several  mouths,  forming  a  delta.     By  the  growth  of  a 
delta  a  delta  plain  is  formed. 


The  flood  plain  of  the  Mississippi  River  i^elow  the  mouth  of  the  Ohio,  ex- 
clusive of  the  delta,  has  an  estimated  area  of  16,000  square  miles.  Its  width, 
between  the  high  banks  or 
bluffs,  varies  from  20  to  80 
miles.  The  area  of  the  Mis- 
sissippi delta  is  approximately 
1 2,300  square  miles.  The  com- 
bined delta  of  the  Ganges  and 
Brahmaputra  rivers  is  of  very 
great  size,  some  estimates 
reaching  50,000  to  60,000 
square  miles.  The  typical  delta, 
shaped  like  the  Greek  letter  of 
that  name,  is  that  of  the  Nile. 
Its  area  is  about  9000  square 
miles.  These  illustrations  serve 
to  show  the  magnitude  of 
river  deposits.  Even  where 
true  deltas  are  not  formed  the 
extension  of  the  coastal  plain 
seaward  by  river  action  is  seen 
in  the  formation  of  delta  shore 
lines. 

The  Nile  Valley  and  that  of 
the  Menam  in  Siam  are  annu- 
ally overflowed,  and  covered, 
when  the  flood  subsides,  with  a 
fine  sedimentary  deposit.  This 
consists  of  rich  fertilizing  mate- 
rials brought  down  from  distant 
mountain  slopes.  It  imparts 
perennial  fertility.  It  has  clothed 
the  land  of  Egypt  with  verdure 
since  the  days  of  the  Pharaohs, 
thousands  of  years  ago.  It  se- 
cures the  great  rice  crop  of  Siam. 


Delta  Shore  Lines  of  the  Gulf  Coast 

Hy  the  deposition  of  waste,  stripped  from  the  higlier 
lands  by  the  Brazos,  A,  the  Colorado,  B,  and 
the  Rio  Grande,  C,  the  coastal  plain  has  been 
extended  gulfward,  giving  rise  to  "  delta  shore 
lines."  r,  Galveston  ;  2,  Matagorda  Bay;  3,  Cor- 
pus Christi  Bay  ;  4,  Laguna  Madre. 

Attention  is  also  called  to  the  long,  sandy,  reef-like 
islands  inclosing  the  bays  and  lagoons. 


Streams  emptying  into  lakes  tend  to  fill  them  with  deposits 
of  gravel,  sand,  and  mud,  while  in  smaller  bodies  of  water  the 


8o 


RELIEF  OF  THE   LAND 


growth  of  vegetation  is  considerable.  If  above  the  sea  level, 
the  outlets  of  these  lakes  are  gradually  lowered  by  erosion  and 
in  the  course  of  time  they  are  drained.  In  this  manner  many 
lake  plains  have  been  formed.  In  some  instances  the  drainage 
of  lakes  may  not  be  complete,  or  the  exposure  of  the  lake  de- 


Al     Fl,i.)(ll> 


posits  may  be  due  to  the  warping  of  the  earth's  crust.  In  such 
cases  the  level  areas  exposed  along  the  shore  are  also  desig- 
nated as  lake  plains.  In  some  parts  of  the  world,  too,  lake  plains 
have  resulted  from  desiccation,  or  the  drying  up  of  the  lake 
waters,  due  to  climatic  changes.  Where  arid  conditions  still 
prevail,  these  old  lake  bottoms  now  form  desert  plains. 

Interior  or  Inland  Plains  are  those  lying  within  the  continents. 
More  or  less  inclosed  by  mountains  and  drained  by  large  rivers, 
they  partake  of  the  general  character  of  valleys,  but  are  on  a 
grander  scale.  Their  origin  is  not  due  to  river  action,  but  rather 
to  the  great  forces  of  upheaval  whereby  continents  have  been 


BASE   LEVEL   AND    PENEPLAINS  8 1 

elevated  and  mountains  formed.  Broadly  speaking,  the  surface 
of  these  plains  is  rolling  or  undulating,  but  many  areas  of  con- 
siderable extent  are  quite  level.  The  great  central  plain  of 
North  America,  lying  in  the  basins  of  the  Mississippi  and  Mac- 
kenzie rivers,  and  the  combined  plains  of  the  Orinoco,  Amazon, 
and  Plata  rivers  in  South  America,  afford  excellent  examples  of 
this  class. 

That  portion  of  the  interior  plain  of  the  United  States  lying  at  the  base  of 
the  Rocky  Mountains  is  known  as  the  ''Great  Plains."  It  is  treeless,  owing  to 
the  arid  conditions  prevailing  there,  and  on  account  of  its  unusual  altitude  is 
often  classed  as  a  plateau.  While  its  appearance  is  that  of  an  extended  prairie 
region,  it  should  not  be  confounded  with  the  true  prairies  lying  at  a  lower 
altitude  and  nearer  the  Mississippi  River.  They  are  fertile  areas  of  treeless 
land  susceptible  of  high  cultivation. 

Base  Level  and  Peneplains.  —  When  a  stream  has  cut  its 
channel  down  to  the  level  of  the  body  of  water  into  which  it 
empties,  it  can  excavate  its  bed  no  deeper.  It  has  reached  its 
lowest  point,  or  base  level.  Such  a  stream,  if  it  flows  across  a 
plain,  will  now  begin  to  meander,  cutting  away  its  banks  later- 
ally. As  this  proceeds,  the  inequalities  of  the  plain  will  even- 
tually disappear  until  the  plain  itself  is  base-leveled. 

To  indicate  a  stage  preceding  that  just  described,  in  which 
the  divides  between  the  streams  may  still  be  recognized  as  low, 
rounded,  but  inconspicuous  hills  and  swells,  the  term  peneplain 
(almost  a  plain)  is  employed. 

It  has  frequently  happened  in  geologic  time  that  plains,  plateaus,  and  even 
mountains,  by  the  incessant  action  of  the  erosive  agents,  have  been  reduced 
to  the  peneplain  or  base-level  state. 

Plains  the  Centers  of  Civilization.  —  Owing  to  their  fertility 
and  ease  of  cultivation,  plains  have  been,  throughout  the  history 
of  man,  centers  of  population,  civilization,  and  power.  The 
imperial  glory  of  Nineveh  and  Babylon,  the  culture  of  ancient 
Egypt,  the  enduring  prosperity  of  China,  and  the  unrivaled 
wealth  of  India,  all  owe  their  origin  to  the  rich  soil  brought  by 
the  rivers  from  the  hills. 


82  RELIEF   OF   THE    LAND 

Plateaus  or  Table-lands  are  broad,  elevated  uplands.  As 
stated  by  Gilbert,  "they  may  be  indefinitely  bounded;  they 
may  be  limited  on  all  sides  by  cliffs  overlooking  adjacent  areas ; 
or  descending  cliffs  may  limit  on  one  side  and  ascending  cliffs 
or  slopes  on  the  other."  The  names  employed  suggest  flat- 
ness. Some  plateaus,  as  the  Llano  Estacado  of  Texas,  are  as 
level  as  the  prairies.  Generally,  however,  plateaus  present  a 
highly  diversified  surface,  hills  and  even  great  mountains  rising 
from  them. 

The  plateau  of  Tibet  consists  of  plains  and  wide  basins,  some 
of  which  contain  large  lakes,  engirdled  by  ranges  of  gigantic 
snow-clad  mountains. 

The  aspect  presented  also  by  the  great  plateau  lying  between 
the  Rocli^  Mountains  and  the  Sierra  Nevada  in  our  own  country, 
is  that  of  a  vast  uplifted  mass  from  which  the  mountains  rise ; 
while  the  Bolivian  plateau,  in  South  America,  with  the  tower- 
ing peaks  of  the  Andes  embosoming  its  upland  lake,  singularly 
resembles  the  plateau  of  Tibet. 

In  elevation  plateaus  vary  greatly.  Low  plateaus,  like  the 
desert  of  Sahara,  are  from  looo  to  3000  feet  in  height.  The 
loftiest  in  the  world  are  the  plateau  of  Tibet,  10,000  to  15,000 
feet  high,  and  the  Bolivian  plateau,  averaging  about  12,000 
feet. 

Kinds  of  Plateaus.  —  According  to  their  origin  plateaus  may 
be  divided  into  two  groups:  diastropJiic  plateaus,  those  result- 
ing from  the  great  forces  of  upheaval ;  and  vulcanic  plateaus, 
those  resulting  from  the  outpourings  of  molten  rock  or  lava. 

Diastrophic  plateaus,  like  the  plains  bordering  the  continents, 
have  been  elevated  above  the  level  of  the  sea.  In  many 
instances  they  are  composed  of  stratified  rock,  sandstones,  lime- 
stones, and  shales.  Oftentimes  the  strata  or  layers  have  suf- 
fered little,  if  any,  displacement,  the  whole  area  having  been 
lifted  bodily.  In  some  regions,  however,  the  rocks  have  been 
broken,  by  faulting,  into  great  blocks,  now  arranged  like  a  series 
of  steps,  each  of  which  gives  rise  to  a  plateau  of  a  different 
altitude.     This    structure  is  particularly    characteristic    of    the 


KkOSION    (>K    HIAIEAUS 


83 


plateaus  trenched  by  the  Grand  Canyon  of  the  Colorado  River 
in  Arizona,  which   have  been  termed  broken  plateaus. 


Sed  Level" 


Broken  Plateaus 

Part  of  a  section  from  west  to  east  across  the  plateaus  north  of  the  Grand  Canyon  of  the 

Colorado.     P'lom  Powell. 

Vulcanic  plateaus  have  been  formed  by  the  coolinc^  of  great 
lava  floods.  In  the  best-known  examples  the  molten  rock 
seems  to  have  welled  up  through  fissures  in  the  crust  now  com- 
pletely concealed  beneath  the  successive  outpourings. 

In  the  northwestern  part  of  the  United  States  there  is  a  vast 
area,  not  less  than  150,000  square  miles  in  extent,  embracing 
portions  of  northern  California,  Nevada,  Idaho,  Oregon,  and 
Washington,  covered  with  these  surface  flows  or  sheets.  Where 
cut  by  the  Columbia  River  the  aggregate  thickness  of  the  sheets 
composing  this  plateau  is  found  to  exceed  3000  feet. 

Erosion  of  Plateaus.  —  By  the  action  of  rain  and  flowing 
water  plateaus  are  gradually  worn  away,  or  eroded. 

Streams  originating  upon  or  crossing  a  recently  elevated 
table- land  deepen  their  channels  until  canyonlike  valleys  are 
formed.     In  this  manner  a  plateau  is  dissected. 

As  the  stream  wear  continues,  tributaries  are  extended,  canyon 
walls  undermined,  and  valleys  broadened.  In  the  meantime  the 
intervening  land,  or  ridges,  assume  somewhat  of  a  mountainous 
aspect,  the  rather  uniform  sky  line  serving  in  a  general  way  to 
indicate  the  surface  of  the  former  plateau.  As  stream  dissec- 
tion and  erosion  continue,  the  ridges  become  lower  and  less  con- 
spicuous   until  they  finally  disappear,   save   here  and  there   a 

M.-S.  PHYS.  GEOG.  —  6 


84 


RELIEF   OF  THE   LAND 


flat-topped  hill,  or  mesa,  capped  with  a  layer  of  hard,  resisting 
rock.     The  plateau  has  now  reached  the  zvorn-doivn  stage. 

Plateaus  cut  by  canyon  valleys  may  be  classed  as  young ; 
those  well  dissected  by  stream  ways,  with  intervening  hills  or 
"mountains,"  as  viature ;  and  the  worn-down  plateau,  as  old. 


The  Bad  Lands  of  South  Dakota 
Illustrating  the  effects  of  erosion  upon  soft  rocks  in  an  arid  region.     Unprotected  by  vege- 
tation, the  valley  vi'alls  are  readily  sculptured   by  water  action   notwithstanding  the 
scanty  rainfall. 


Plateaus  Unproductive.  —  The  plateau  regions  of  the  world 
are  for  the  most  part  unproductive.  Many  of  them  are  absolute 
deserts.  Hence  few  plateaus  have  ever  become  centers  of 
population  and  power.  It  is  interesting,  however,  to  observe 
that  the  table-lands  of  Mexico,  Peru,  and  Tibet  have  each  been 
the  seat  of  a  civilization  peculiarly  its  own. 


MOUNTAINS 


85 


The  desert  plateaus  have  undoubtedly  their  part  to  perform  in  the  economy 
of  nature.  They  are  not  wastes  in  the  sense  of  being  wasted  or  useless  areas. 
Their  effect  upon  the  rainfall  and  its  distribution  is  most  important.  It  will 
be  more  fully  considered  when  we  treat  of  the  moisture  of  the  air. 


The  Matiekiiokn,  or  Mont  Cekvin 
This  celebrated  peak  has  an  altitude  of  14.705  feet.     From  stereograph.     Used  by  per- 


Mountains.  — The  higher  and  more  conspicuous  elevations  of 
the  earth's  crust  are  termed  mountains.  Although  they  some- 
times stand  singly,  as  Etna  or  Vesuvius,  more  often  they  are 


86 


RELIEF   OF  THE   LAND 


joined  together  in  the  form  of  a  connected  series  called  a  range 
or  chain.  Mountain  chains  seldom  occur  solitary.  Usually 
two  or  more  are  parallel,  or  nearly  so,  forming  a  mountain 
system.  Of  this  the  Andes,  the  Alps,  and  the  Appalachians 
afford  striking  examples. 

Descriptive  Terms.  —  Isolated  summits  are  called  peaks.  The 
top  of  a  ridge  from  which  there  is  a  descent  in  opposite  direc- 
tions is  known  as  a  crest.  The  slopes  of  a  ridge  or  peak  con- 
stitute its  flanks.  A  ridge  or  group  of  ridges  presenting  a 
serrated  or  notched  sky  line  is  called  a  sierra.  Sharp-pointed 
peaks  are  spoken  of  as  horns,  a  term  especially  used  in  Alpine 
regions. 

The  Formation  of  Mountains.  —  Mountains  have  been  formed 
in  at  least  four  ways  :  by  folding  or  crumpling,  by  faulting, 
by  vulcanism,  and  by  erosion. 


.\  Representation  of  the  Effects  of  Contraction  upon  an  Outer,  Yield- 
ing Spherical  Covering 

In  A  the  interior  of  the  sphere,  a,  is  shown  before  coniractit>n.  The  coat  b  fits  closely 
upon  if.  In  B  the  interior  of  the  sphere,  a,  is  shown  after  contraction.  The  non- 
shrinking  coat,  h,  in  order  to  fit  upon  it  is  now  thrown  into  folds.  The  amount  of 
contraction  is  shown  V)v  a  comparison  of  Ihe  radius  in  .  /  with  that  in  B. 


(i)  The  folding  process  is  thought  to  be  a  result  of  contrac- 
tion. The  crust  of  the  earth  is  regarded  as  a  spherical  shell 
or  coat,  now  practically  cool,  surrounding  a  heated,  but  cooling 


rHK    l-oRMMIoN    ()!•     NKjL'NIAINS 


87 


and  therefore  shrinking,  interior.  Under  the  influence  of  grav- 
ity the  crust  is  drawn  downward,  that  is,  toward  the  center  of 
the  earth,  and  thus  a  larger  spherical  surface  is  made  to  fit 
closely  upon  a  smaller.  This  can  be  brought  about  only  by 
the  folding,  crushing,  and  breaking  of  the  crust. 

Although  serious  objections  have  been  brought  against  this 


An    Ui'WARu    Fold   of  the    Ea kin's    Ckust    (Anticlink),  near    Hancock, 

Maryland 


theory,  the  fact  remains  that  many  of  the  most  prominent 
mountain  systems  are  composed  of  folded,  crushed,  and  dis- 
turbed strata,  as  is  well  exemplified  in  the  Appalachian  and 
Jura  Mountains. 

(2)  In  the  region  of  the  Great  Basin,  between  the  Sierra 
Nevada  and  the  Rocky  Mountains,  there  is  found  a  type  of 
mountain  structure  due  primarily  to  faulting :  long,  narrow 
ridges  with  a  cliff,  or  scarp,  on  one  side  and  a  gentle  slope  on 
the  other.  Here  it  would  seem  that  a  great  plain  had  been  up- 
heaved in  the  form  of  a  mighty  dome  which,  owing  to  tension, 
or   stretching,    was    traversed  by  numerous  cracks  or  fissures. 


RELIEF   OF  THE   LAND 


Finally,  by  the  collapse  of  the  dome,  the  long,  narrow,  parallel 
blocks  were  displaced  or  faulted  and  each  became  a  mountain 
ridge. 

(3)  The  formation  of  ordinary  vulcanic  mountains  has  already 


Diagrammatic  Illustration  of  Block  Mountains 
The  tilted  blocks  are  carved  into  hills,  and  mountains  and  cut  by  narrow,  canyon-like 
gojges,  while  the  valleys  between  them  are  filled  with  wash,  sand  and  gravel,  brought 
down  from  the  adjacent  heights.    The  streams  in  such  a  region  either  are  lost  in  the 
sands  or  flow  into  lakes,  permanent  or  temporary. 

been    illustrated  in  the  description  of  volcanoes,  the  cones  of 
which  are  built  up  by  the  ejectment  of  cinders   and  ash,  the 

outpouring  of  lava, 
or  by  both  of  these 
processes. 

There  is,  however, 
a  type  of  vulcanic 
mountain  of  quite  a 
different  structure. 
Through  a  fissure, 
or  conduit,  in  the 
earth's  crust,  not 
reaching  the  surface, 


Ideal  Section  of  a  Laccolite. 
S,  sheets ;  D,  dikes. 


After  Gilbert. 


molten  matter  from  below  has  been  forced,  which,  spreading 
out,  lifts  the  overlying  strata  bodily  upward  in  the  form  of  a 
dome.     Later  this  elevation  is  eroded  or  worn  away,  exposing 


VALLEYS 


89 


in  many  places  the  interior  igneous  filling,  known  as  a  laccolite. 
Such  mountains  are  said  to  have  a  laccolitic  structure. 

(4)  As  already  stated,  dissected  plateaus  may  give  rise  to  a 
rugged  country.  Here  the  mountains  may  be  flat-topped,  with 
summit  scarps  or  cliffs,  and  sloping  flanks  covered  with  rock 
waste  (talus),  or  they  may  be  rounded  off  and  subdued  as  in 


The  Border  of  the  Edwards  Plateau  on  the  Colorado  River,  West  of 

Austin,  Texas 


the  region  of  the  Allegheny  plateau  bordering  the  Appalachian 
Mountains  on  the  west. 

Valleys  are  depressions  through  which  usually  water  courses 
run.  Every  mountain  range  is  intersected  by  valleys,  and  every 
mountain  system  has  valleys  separating  its  parallel  ranges.  The 
valleys  intersecting  ranges  are  called  transverse.  Those  lying 
between  parallel  ranges,  and  having  therefore  the  same  general 
direction,  are  called  longitudinal. 

In  regions  of  folded  mountains  the  formation  of  valleys  is 
largely  due  to  the  upheavals  and  depressions  which  have  dis- 
turbed the  surface  of  the  earth.     The  formation  of  valleys  is 


90    . 


KELIKF   OF   THE    LAND 


Grand  CamvoxN  of  the  Colorado 


really  a  part  of  the  process  by  which  mountains  are  made. 
The  action  of  running  water  has,  of  course,  widened  and 
deepened  them. 

Valleys  traversing  plains  and  plateaus  have  been  formed  by 


GENERAL    ELEVATION   OF  THE    LAND 


91 


the  erosive  action  of  water.     Of  such  valleys  the  most  extraor- 
dinary in  the  world  are  the  canyons  of  our  Western  rivers. 

That  of  the  Colorado  is  a  gorge  shut  in  by  ahnost  perpendicular  walls  of 
rock.  It  is  from  3000  to  6000  feet  in  depth  and  300  miles  long.  Canyons 
are  among  the  most  impressive  evidences  of  the  age  of  our  earth.  Thousands 
of  years  would  be  a  brief  period  for  the  work  of  wearing  away  solid  rock  by 
running  water  to  the  depth  of  more  than  a  mile  as  in  the  case  of  the  (irand 
Canvon  of  the  Colorado. 


A  Watkr  Gap 

The  Narrows  of  Wills  Mountain,  Maryland.    Cumberland  in  the  foreground. 

From  Geological  Survey  of  Maryland. 

The  heading  together  of  transverse  vallcNs  renders  it  possible 
to  cross  lofty  mountain  ranges.  Human  ingenuity  and  indus- 
try have  improved  these  natural  courses  of  travel,  or  passes,  as 
they  are  called,  and  some  of  them  have  been  made  marvels  of 
engineering  skill.  The  Simplon,  Saint  Bernard,  and  Saint  Go- 
thard  passes,  crossing  the  Alps,  are  among  the  most  noted.  The 
Alpine  railroad  tunnels  have,  to  a  large  extent,  taken  the  place 
of  the  passes.  In  the  eastern  portion  of  the  United  States  the 
narrow  transverse  valleys,  through  which  streams  flow,  are 
termed  li'ater gaps. 

General  Elevation  of  the  Land.  —  Among  the  best  evidences 
of    continental    elevation    are    those    furnished    by    raised    sea 


92 


RELIEF  OF  THE   LAND 


beaches,  water-worn  caves,  and  terraces  now  found  far  above 
the  seat  of  wave  action,  and  by  the  occurrence,  at  various 
elevations,  of  coral  reefs  and  the  shells  of  marine  animals 
still  adhering  to  the  rocks  upon  which  they  grew. 

In  some  parts  of  Great   Britain  (geologically  a  part  of  the 
Eurasian  continent)  raised  sea  beaches,  five  or  six  in  number, 

are  found  at  different 
levels  up  to  lOO  feet, 
and  on  the  Norwe- 
gian coast  there  are 
numerous  ice-cut  ter- 
races, which  repre- 
sent successive  old 
shore  lines.  Modern 
coral  rock  has  been 
reported  by  Alexan- 
der Agassiz  as  occur- 
ring in  Peru  at  the 
height  of  3000  feet 
above  the  sea  level, 
and  raised  coral  reefs 
are  found  in  several 
places  fringing  the 
Red  Sea. 

The  above  are  a 
few  of  the  many  ex- 
amples that  could  be 
cited  illustrating  the 
elevation  of  the  land  masses  with  reference  to  the  sea  level. 
General  Subsidence  of  the  Land.  —  In  many  parts  of  the 
world  there  is  evidence  of  the  sinking  or  subsidence  of  the 
land.  This  is  shown  in  drowned  valleys,  estuaries,  and  fiords, 
and  in  the  submerging  of  forests  as  well  as  of  the  works  of  man. 
The  sinking  of  the  west  coast  of  Greenland  is  a  familiar 
example.  Here  the  inhabitants  fasten  their  boats  to  poles  or 
piles  driven  off  the  shore.     After  long  intervals,  by  the  subsi- 


A  iJKDWNKi)  River  —  Chesapeake  Bay 


CAUSES   OF   RELIEF 


93 


dence  of  the  bottom,  the  poles  disappear  beneath  the  surface 
of  the  water  and  must  be  reset. 

The  stumps  of  cypress  trees  show  submerged  forest  land  on 
the  coast  of  South  Carolina  and  Georgia;  and  near  the  head 
of  the  Bay  of  Fundy,  in  Cumberland  County,  Nova  Scotia,  the 
stumps  of  pine  and  beech  trees,  still  embedded  in  the  soil  on 
which  they  grew,  are  covered  to  the  depth  of  25  to  35  feet  at 
high  water. 
v*  The  coast  of  New  Jersey  also  may  be  cited  as  a  region  of 


At  the  Head  of  Chesapeake  Bay 
Elk  and  Bohemia  rivers  from  Elk  Neck.     From  Geological  Survey  of  Maryland. 

subsidence,  the  estimated  rate  being  about  two  feet  a  century ; 
and  the  estuaries  known  as  the  Hudson  River  and  Chesapeake 
Bay  represent  the  drowning  of  former  river  valleys  by  subsi- 
dence. The  fiords  of  the  northern  coasts  furnish  examples 
of  the  invasion  of  glaciated  valleys  by  the  sea  due  to  crustal 
sinking. 

Causes  of  Relief. — What  force  or  forces  may  have  caused 
the  general  elevation  of  continents  we  cannot  with  certainty 
tell.  On  the  principle  that  Hke  effects  are  due  to  like  causes 
we  should  conclude  that  the  elevation  of  the  continents  and  the 
formation  of  folded  mountains  were  produced  by  similar  forces ; 
namely,  those  resulting  from  interior  contraction  and  consequent 
crustal  deformation.     Whatever  may  be  our  conclusions  on  this 


94 


RELIEF   OF  THE    LAND 


point,  it  is  clear  that  the  forces  have  been  at  work  for  ages,  at 
times  silently  and  gently,  again  with  sudden  displacements  and 
earthquakes,  raising  some  portions  of  the  earth's  surface  and 
depressing  others. 

Effects  of   Relief.  —  The    elevations  of    the  earth's    surface, 
although  comparatively  insignificant,  are  to  be  regarded  as  im- 


A  Norwegian  Fiord 
Loen  Lake. 


portant  regulators  of  climate.  Not  many  hundred  feet  added  to 
the  relief  of  a  country  would  suffice  to  alter  its  physical  aspects 
entirely,  converting  vineyards  into  pasture  lands,  or  pasture  lands 
into  regions  of  perpetual  snow.  Reverse  changes  would  result 
from  a  corresponding  diminution  in  the  average  elevation. 

Again,  relief  is  the  great  regulator  of  drainage.  If  the  sur- 
face of  the  earth  had  been  a  dead  level,  without  hills,  plateaus, 
and  mountains,  there  would  have  been  no  water  courses.  The 
whole  land  would  have  been  one  broad  marsh  incapable  of 
drainage,  and  unsuited  for  human  occupation. 


X.    RELIEF    FORMS   OF    NORTH    AND    SOUTH 
AMERICA 

General  Features  of  Continental  Relief.  —  There  are  certain 
features  of  relief  that  belong  to  all  the  grand  divisions  of  the 
continents:  i.  They  are  bordered  by  mountains.  2.  They  are 
traversed  in  the  direction  of  their  greatest  length  by  a  great  moun- 
tain system.  3.  In  each  there  is  usually  a  subordinate  mountain 
system.     4.    In  each  there  is  usually  a  depressed  central  area. 

The  line  of  direction  taken  by  the  principal  mountain  ^system 
is  termed  the  superior  or  main  axis  of  elevation.  This  line  is 
not,  however,  in  any  case  centrally  placed,  as  the  word  axis 
might  seem  to  imply,  but  far  to  one  side  of  the  grand  division, 
which  it  thus  divides  into  two  unequal  slopes.  The  subordinate 
mountain  system  follows  the  inferior  axis  of  elevation. 

North  America  conforms  closely  to  the  general  principle  of 
continental  relief.  It  has  a  superior  and  an  inferior  highland, 
between  which  there  is  a  rather  low,  basin  like  interior. 

The  superior  highland  is  known  as  the  Pacific  highland,  the 
inferior  as  the  Atlantic  highland,  and  the  interior  region  as  the 
great  central  plain. 

While  these  three  divisions  constitute  the  main  features  of 
relief,  when  considered  more  in  detail  it  will  be  found  that  they 
include  many  topographic  forms  which  give  rise  to  surface 
expressions  characteristic  of  the  grand  division. 

The  Pacific  Highland  extends  from  the  Isthmus  of  Panama  to 
the  Arctic  Ocean.  Its  general  course  is  northwest  and  south- 
east. Its  inner  border,  facing  the  interior  of  the  continent,  con- 
sists of  many  mountain  ranges  with  lofty  peaks,  which  are 
collectively  known  as  the  Rocky  Moiin^ins.  Its  outer  border, 
facing   the    Pacific  Ocean,  also    consists^  of    mountain    ranges, 

95 


96  RELIEF    l-ORMS   OF   NORTH    AND    SOUTH    AMERICA 


The  Relief  of  North  America 
The  heavy  black  lines  upon  this  and  the  following  maps  represent,  in  a  general  way,  the 
extent  and  direction  of  the  mountain  chains.     The  elevations  and  depressions  are  indi- 
cated by  the  buff  and  green  colors.     The  buff,  according  to  the  depth  of  its  tint,  repre- 
sents elevations  of  greater  or  less  altitude.     The  green  indicates  lowlands. 


THE    K(K"KV    MOUNIAINS 


97 


chiefly  the  Sierra  Nevada  and  the  Cascade  Mountains.  Be- 
tween the  boundaries  here  given,  within  the  territory  of  the 
United  States,  lies  an  elevated  plateau  region,  which  consists 


SIERR4   NEVADA 


APRALACHIIN    MTS. 


Profile  of  North  America  from  West  to  East 

of  three  physiographic  divisions :  the  Columbia  plateau,  or 
that  drained  by  the  Columbia  River;  the  Great  Basin,  or  that 
with  an  interior  drainage  represented  by  such  streams  as  those 
flowing  into  the  Great  Salt  Lake  and  the  Sink  of  the  Humboldt 
River ;  and  the  Colorado  plateau,  or  that  drained  by  the  upper 
and  middle  portions  of  the  Colorado  River  of  the  West. 


■■ 

^^^^^^^^^^^m 

B^H^B 

A  Rocky  Mountain  Summit— Pikes  Peak 

The  Rocky  Mountains  exhibit  great  variation  in  structure. 
Many  of  the  ranges  seem  to  have  resulted  from  the  upheaval 
of  the  older  or  crystalline  rocks,  shouldering  off  the  stratified 
rocks  which  now  rest  upon  their  flanks    in    a    highly  inclined 


98 


RELIEF   FORMS   OF   NORTH   AND   SOUTH   AMERICA 


position.  This  is  especially  true  of  the  ranges  facing  the  Great 
Plains.  Mountains  have  also  resulted  from  crushing,  folding, 
and  faulting,  and  the  evidence  of  igneous  action  is  not  wanting. 
The  magnitude  of  the  Rocky  Mountains  will  be  better  under- 
stood when  it  is  known  that  within  the  state  of  Colorado  alone 
there  are  30  or  more  peaks  each  having  an  altitude  exceeding 
two  and  one  half  miles. 

The  whole  region  of  uplift  has  been  cut  and  carved,  worn, 
and  remodeled  by  the  action  of  snow  and  ice  (glaciers),  rain, 


Gateway,  Garden  of  the  Gods,  Colorado 


and  flowing  water.  Thus  the  present  form  of  these  mountains 
has  been  wrought  —  the  peaks,  domes,  and  ridges.  Rising 
above  the  timber  line,  the  higher,  barren,  rocky  summits,  ex- 
posed to  the  wasting  action  of  the  elements,  are  covered  with  a 
mantle  of  coarse  fragments  —  they  are  rocky  mountains  in  fact 
as  well  as  in  name. 

^\\^  parks  and  gardens  are  features  worthy  of  special  mention. 
The  former  are  sheltered  valleys,  surrounded  by  mountains, 
the  best  known  being  North,  Middle,  South,  and  San  Luis 
parks;  the  latter  are  valleys  of  erosion  formed  by  the  wasting 


THt    ROCKY    MOUNTAINS 


99 


away  of  the  softer  portions  of  the  upturned  strata  on  the  flanks 
of  the  mountains,  the  harder  strata  forming  an  inclosing  wall. 
The  Garden  of  the  Gods,  at  the  foot  of  Pikes  Peak,  near  Colo- 
rado Springs,  and  Monument  Park  furnish  excellent  examples 
of  the  effects  of  erosion  on  strata  of  varying  degrees  of  hard- 
ness. 

Within  the  Dominion  of  Canada  the  Rocky  Mountains  still 
rise  as  a  lofty  barrier  between  the  great  central  plain  and  the 


The  Bridge  of  Sighs  —  an  Example  of  Erosion,  Monument  Park,  Colorado 

Pacific  Ocean.  Here  are  found  numerous  living  glaciers  spread- 
ing from  the  snow-clad  summits.  Being  nearer  the  Pacific, 
these  mountains  are  more  bountifully  watered  than  the  ranges 
within  the  United  States,  and  consequently  more  heavily 
timbered. 


Many  large  rivers  have  their  sources  in  the  Rocky  Mountains.  The  Missouri 
and  Arkansas  and  their  numerous  tributaries,  together  with  the  Rio  Grande, 
represent  the  Gulf  drainage.  The  Fraser  River  in  Canada,  the  Columbia,  and 
the  Colorado  have  their  origin  on  the  west  side  of  the  mountains.  The  latter 
rivers  are  remarkable  for  the  depth  to  which  they  have  excavated  their  chan- 
nels in  their  course  to  the  sea.  Plateaus  and  even  mountains  have  been 
deeply  trenched,  forming  the  most  wonderful  canyon  gorges  in  the  world. 


lOO  RELIEF   FORMS   OF   NORTH    AND  SOUTH    AMERICA 

The  Sierra  Nevada  and  Cascade  Ranges  form  the  western  but- 
tress of  the  Pacific  highland.  The  Sierra  Nevada  lies  within 
the  state  of  California,  extending  from  Mount  Shasta,  near  its 
northern  boundary,  in  a  southeastern  direction,  skirting  the 
valleys  of  the  Sacramento  and  San  Joaquin  rivers  ;  the  Cascade 
Mountains  extend  northward  from  Mount  Shasta  through  the 
states  of  Oregon  and  Washington  into  the  Dominion  of  Canada, 
following  a  course  parallel  to  the  Pacific  coast. 

The  Sierra  Nevada  ranges  have  an  interesting  history. 
Originally  elevated  by  a  crumpling  of  the  earth's  crust,  they 
were  eroded  until  represented  by  mountains  of  very  low  altitude. 
Later  they  again  became  the  scene  of  a  great  upheaval.  Faulted 
and  broken  into  great  blocks,  their  crest  was  moved  farther  east- 
ward and  the  rugged  mass  left  with  a  steep  slope  facing  the 
east  and  a  rather  moderate  declivity  facing  the  west.  This 
second  elevation  was  accompanied  by  lava  floods  which,  issuing 
from  great  rents  and  fissures,  coursed  down  the  mountain  sides, 
filling  the  old  river  channels.  As  a  consequence  of  this  a 
readjustment  of  the  streams  followed  and  new  valleys  were 
excavated. 

Between  Lake  Tahoe  and  Owens  Lake  the  Sierra  Nevada 
attains  its  greatest  altitude,  culminating  in  Mount  Whitney.  To 
the  highest  portion  of  this  region  the  name  of  HigJi  Sierra  has 
been  given.  Here  are  found  numerous  living  glaciers  filling 
depressions  or  cirques  on  the  north  side  of  high  summits.  They 
are  all  of  small  size  and  confined  to  altitudes  exceeding  10,000 
feet  above  the  sea  level. 

The  Cascade  Mountains  were  in  the  past  the  seat  of  extensive 
volcanic  action.  Of  the  many  beautiful  cones  which  crown 
their  summit  Mount  Hood  is  probably  the  most  conspicuous. 
The  highest  peaks,  including  Mount  Shasta,  Mount  Hood, 
Mount  Rainier,  Mount  Baker,  and  the  Three  Sisters,  are  snow- 
capped and  support  living  glaciers.  Here  as  in  other  regions 
of  high  altitude  the  upraised  mass  has  been  deeply  dissected. 

The  Columbia  Plateau  is  a  region  of  lava  floods.  The  entire 
area  between  the  Rocky  and  the  Cascade  Mountains  has  been 


THK    (OI.IMISIA    I'l.AIKAU 


lOI 


literally  buried  beneath  a  vast  outpouring  of  igneous  matter, 
forming,  when  cooled,  a  great  lava  plain  from  which,  in  places, 
old  mountain  summits  rise  in  islandlike  masses.  The  flowing 
lava  by  obstructing  the  stream  ways  caused  the  formation  of 
many  lakes.  Later  these  were  drahied  and  their  deposits  now 
form  rich  agricultural  lands. 

In   its    course  through  the  lava  beds,  the  Snake  River,  for 
several  hundred  miles,  has  excavated  a  deep  canyon,  forming  a 


Mt.  Hood  from  Lost  Lake.     Height  11,22^  Feet 


barrier  of  considerable  magnitude.  In  this  gorge  there  are 
points  where  the  irregularities  of  the  older  land  surface  are  en- 
countered ;  these  have  also  been  deeply  eroded  by  stream  wear. 
Near  the  head  of  the  canyon  the  river  flows  over  a  lava  preci- 
pice, forming  a  magnificent  cataract  known  as  Shoshone  Falls. 
That  this  region  has  not  been  entirely  free  from  diastrophic 
movements  is  shown  by  the  Blue  Mountains,  which  have  been 
formed  by  the  breaking  and  upheaval  of  a  portion  of  the  lava 
plain. 

M.-S.  PHYS.  GEOG.  —  7 


I02  RELIEF   FORMS   OF   NORTH   AND    SOUTH    AMERICA 

The  lava  floods  of  the  Columbia  plateau  are  among  the  greatest  known  in 
the  history  of  the  earth.  They  are  exceeded  only  by  those  of  the  peninsula 
of  India. 

The  Great  Basin  includes  a  large  area  lying  between  the 
Wasatch  Mountains  and  the  Sierra  Nevada,  characterized  by 
its  interior  drainage  and  wide-spread  aridity.  Its  width,  in  an 
east-and-west  direction,  is  fully  500  miles  and  its  length  800 
miles.  In  its  northern  portion  it  attains  a  general  altitude  of 
4000  to  5000  feet,  with  mountains  rising  still  higher.  In  its 
southern  portions  its  altitude  is  greatly  reduced,  and  in  Death's 
Valley,  in  southern  California,  it  is  several  hundred  feet  below 
the  sea  level.  Its  surface  is  diversified.  There  are  large,  level 
desert  plains  as  well  as  mountains  and  valleys.  As  has  been 
already  stated,  the  crust  of  the  earth  has  here  been  profoundly 
fractured  and  faulted,  and  the  Basin  ranges,  trending  north  and 


Section  illustrating  the  Structure  of  the  Basin  Ranges.    After  Russell. 

south,  have  resulted  from  the  upheaval  and  tilting  of  the  long, 
narrow  blocks.  As  they  now  rest  they  present  a  precipitous 
front  in  one  direction  and  slope  off  gradually  in  the  other. 
The  valleys  between  the  mountains  have  been  deeply  filled  with 
rock  waste,  which,  issuing  from  the  gorges,  has  spread  out  in  the 
form  of  wide  fans. 

The  streams  of  the  Great  Basin  either  end  in  salt  or  alkaline 
lakes  or  are  evaporated  or  absorbed  before  reaching  them. 
During  times  of  storm  mountain  torrents,  upon  reaching  the 
valleys,  owing  to  their  increased  volume,  spread  out,  forming 
temporary  lakes.  These  soon  evaporate,  and  there  are  left  mud 
plains,  or  playas.  Such  mud  deposits  are  common  in  many 
parts  of  Nevada. 

Formerly  the  amount  of  precipitation  in  this  region  was 
much  greater  than  at  present  and  there  existed  large  lakes  now 


THE   GREAT   BASIN 


103 


extinct.  Their  old  shore  lines  have  been  traced  for  many 
miles  and  their  old  terraces  and  delta  deposits  have  been  care- 
fully studied.  One  of  these  lakes,  of  which  Great  Salt  Lake  is 
a  remnant,  spread  out  over  a  large  part  of  the  western  half  of 
Utah.  It  has  been  named  Lake  Bonneville.  Another  exten- 
sive lake  existed  in  the  northwestern  part  of  Nevada,  of  which 


Map  of  Portions  of  Utah  and  Nevada  showing  the  Areas  formerly 

OCCUPIED   BY  the   EXTINCT   LAKES   BONNEVILLE   AND   LaHONTAN 


Pyramid,  Winnemucca,  Humboldt,  North  and  South  Carson,  and 
Walker  lakes  are  remnants.  To  this  inland  sea  the  name  of 
Lake  Lahontan  has  been  given, 

"  The  bare  mountains  reveal  their  structure  almost  at  a  glance,  and  show  dis- 
tinctly the  many  varying  tints  of  tlieir  naked  rocks.  Their  richness  of  color 
is  sometimes  marvelous,  especially  when  they  are  composed  of  the  purple 
trachytes,  the  deep-colored  rhyolites,  or  the  many-hued  volcanic  tufa  so 
common  in  western  Nevada.  Not  un frequently  a  range  of  volcanic  mountains 
will  exhibit  as  many  brilliant  dyes  as  are  assumed  by  the  New  England  hills  in 
autumn.  On  the  desert  valleys  the  scenery  is  monotonous  in  the  extreme, 
yet  has  a  desolate  grandeur  of  its  own.  and  at  times,  especially  at  sunrise  and 
sunset,  great  richness  of  color.  ...  As  the  sun  sinks  behind  the  western  peaks 
and  the  shades  of  evening  grow  deeper  and  deeper  on  the  mountains,  every 


I04  RELIEF   FORMS   OF   NORTH    AND    SOUTH    AMERICA 

ravine  and  canyon  becomes  a  fathomless  abyss  of  purple  haze,  shrouding  the 
bases  of  gorgeous  towers  and  battlements  that  seem  encrusted  with  a  mosaic 
more  brilliant  and  intricate  than  the  work  of  the  Venetian  artists." 

—  I.e.  RUSSKLL. 

The  Colorado  Plateau  occupies  the  region  between  the  Wa- 
satch and  the  Park  Mountains.  On  the  north  it  is  bounded  by  the 
Uinta  range  and  on  the  south  it  extends  into  Arizona  and  New 
Mexico.  Through  it  the  Colorado  River  has  cut  its  canyon. 
Here  the  earth's  crust  has  been  extensively  faulted,  and  by  the 
upheaval  of  great  blocks,  embracing  many  square  miles  of  area, 
minor  plateaus  have  been  formed.  As  these  blocks  have  been 
slightly  tilted,  their  upturned  edges  form  scarps  or  cliffs,  which, 
by  the  erosion  of  their  softer  layers  or  strata,  have  retreated 
until  the  plateaus  in  places  resemble  a  series  of  steps  or  ter- 
races. The  higher  scarps  rise  a  thousand  feet  or  more,  and 
some  of  them  follow  quite  closely  the  fault  lines.  That  vulcan- 
ism  has  not  been  absent  is  shown  by  the  occurrence  of  cinder 
cones,  laccolitic  mountains,  and  table  mountains  capped  with 
igneous  rock. 

The  Atlantic  Highland  comprises  the  Appalachian  mountain 
system  and  the  plateau  of  Labrador.  It  extends  from  Labrador 
nearly  to  the  Gulf  of  Mexico. 

The  Appalachian  Mountains  in  their  northern  course  consist 
of  a  number  of  disconnected  groups  such  as  the  White  Moun- 
tains of  New  Hampshire,  the  Green  Mountains  of  Vermont,  and 
the  Adirondack  and  Catskill  Mountains  of  New  York.  To  the 
southward  they  are  composed  of  several  well-marked  and  nearly 
parallel  ranges,  separated  into  two  belts  by  the  Great  Appa- 
lachian Valley,  a  pronounced  depression  extending  from  Pennsyl- 
vania to  Alabama.  The  belt  lying  nearer  the  coast  is  composed 
largely  of  older  rocks  in  the  form  of  gneisses,  schists,  and 
granites,  collectively  known  as  crystalline  rocks,  while  the  inner 
belt  is  made  up  of  stratified  rocks,  much  folded,  compressed, 
and  overthrust.  To  hav-e  produced  such  results  it  is  reason- 
able to  suppose  that  the  force  exerted  must  have  been  very 
great. 


iHE  ailantk:  highland 


105 


The  Appalachian  Mountains  also  have  an  interesting  history. 
Originally  elevated  at  the  close  of  the  Carboniferous  or  Great 
Coal-making  period,  they  were  subsequently  much  worn  and 
eroded  until  a  lowland  was  formed.  Then,  at  a  later  period, 
came  reelevation  with  so  slight  disturbance  that  many  of  the  old 
streams  were  able  with  slight  modifications  to  retain  their  former 
courses,  which  now,  much  deepened,  cross  many  mountain  ranges. 


View  in  thk  Southern  Appalachians 

Richland  Valley  from  Junaluska  Mountain,  North  Carolina.     From  United  States  Geo- 
logical Survey. 

Such  is  notably  the  case  with  the  Susquehalina,  Potomac,  James, 
and  New  rivers.  In  the  meantime  the  tributaries  of  these 
streams  have  been  very  active  removing  the  softer  and  more 
soluble  rocks,  thus  leaving  the  harder  rocks  in  relief.  In  this 
manner,  rather  than  by  folding,  the  existing  ridges  have  been 
produced. 

The  general  elevation  of  the  Appalachians  is  about  3000  feet 
above  the  sea,  but  the  culminating  points.  Mount  Mitchell,  in 
North  CaroHna,  and  Mount  Washington,  in  New  Hampshire, 
are  over  6000  feet  high.^ 

1  Mount  Mitchell,  671 1  feet;    Mount  Washington,  6279  feet. 


I06         RELIEF   FORMS   OF   NORTH    AND    SOUTH    AMERICA 


The  Relief  of  South  America 


riii:  iKMKAi.  ri.Aix  107 

Toward  the  interior  the  Apijalachiaiis  are  bordered  by  more 
or  less  dissected  uplands  known  as  the  Allegheny  plateau;  on 
the  seaward  side  they  descend  to  the  gentle  undulating  Piedmont 
belt,  which,  si)uth  of  New  England,  is  followed  bv  a  rather  broad 
coastal  plain. 

The  Central  Plain  extends  from  the  Gulf  of  Mexico  to  the  Arc- 
tic Ocean.  The  Height  of  Land,  a  low  east-and-west  ridge  near 
the  northern  boundary  of  the  United  States,  divides  it  into  two 
parts.  The  drainage  of  the  northern  portion  is  to  the  Arctic  Ocean 
and  Hudson  Bay  ;  that  of  the  southern  portion  is  to  the  Gulf  of 
Mexico.  As  the  streams  of  the  latter  part  are  mainly  tributary 
to  the  Mississippi  River,  it  is  usually  known  as  the  Mississippi 
basin. 

Tlie  .Mississippi  basin  bears  a  strikinij  resemblance  to  a  coastal  plain.  It 
occupies  the  site  of  an  ancient  interior  sea.  As  the  crust  here  has  never 
suffered  .serious  disturbance,  there  is  a  complete  absence  of  the  more  striking 
features  of  relief.  As  far  south  as  the  mouth  of  the  Ohio  River  this  region  has 
been  subiected  to  glacial  action  (see  page  269).  The  soils  are  deep  and  very 
fertile.  They  have  originated  in  part  from  materials  transported  by  glaciers, 
in  part  from  stream  and  lake  deposits,  and  in  part  from  the  wasting  of  rocks 
due  to  weathering.  In  the  middle  West  there  are  large  areas  of  prairie  land, 
some  e.xceedingly  level,  others  rolling.  On  the  east  the  prairies  merge  with 
the  wooded  region  as  they  approacli  tlie  Allegheny  plateau,  and  on  the  west 
they  pass  imperceptibly  into  the  higher  or  Great  Plains  region.  Along  prairie 
streams  there  is  usually  a  rather  luxuriant  growth  of  trees  and  vines. 

South  America.  —  The  general  features  of  relief  as  exhibited 
by  South  America  are  similar  to  those  of  North  America. 
There  is  a  superior  or  Pacific  highland  and  an  inferior  or  At- 
lantic highland,  with  low  central  plains  between  them. 

The  Pacific  highland  includes  the  Andes  Mountains,  with  their 
long,  high  valleys,  and  the  lofty  BoHvian  plateau.  The  Atlan- 
tic highland,  severed  by  the  valley  of  the  Amazon,  includes  the 
Guiana  and  Brazilian  highlands. 

By  many  the  Andes  are  regarded  as  the  direct  continuation  of  the  Pacific 
highland  of  North  .America,  which,  in  crossing  the  Isthmus  of  Panama,  is 
reduced  to  a  series  of  rather  low  hills. 


■%i*. 


I08  RELIEF   FORMS   OF  NORTH   AND   SOUTH   AMERICA 

While  such  close  relationship  cannot  be  established  between  the  Atlantic 
highlands  of  the  two  grand  divisions,  each  includes  in  its  make-up  crystalline 
and  the  older  stratified  rocks. 

The  Andes  are  remarkable  for  their  great  length,  equal  to  one 
sixth  of  the  earth's  circumference,  for  their  height,  and  for  their 
regularity  of  form.  South  of  Aconcagua  these  mountains  con- 
sist of  a  single  chain,  the  highlands  of  the  coast  being  separated 
from  them  by  a  broad  valley.  Farther  south,  owing  to  subsi- 
dence, the  higher  parts  of  the  western  ridges  appear  as  islands 
and  peninsulas.  Between  27°  south  latitude  and  the  equator 
parallel  eastern  and  western  ranges  inclose  valleys  and  plateaus, 

,0  ftlllimani 


BRAZILIAN    HIGHLAND 


Profile  ok  South  America  from  West  to  East 

wonderful  in  height  and  extent,  separated  by  transverse  ranges 
or  mountain  knots.  Of  the  table-lands,  the  Bolivian  plateau  is 
broadest  and  highest,  and,  like  the  Great  Basin  of  North  Amer- 
ica, has  an  interior  drainage.  Upon  it  is  situated  Titicaca,  the 
largest  lake  in  South  America  and  the  highest  in  the  western 
hemisphere. 

North  of  the  Desert  of  Atacama  to  the  center  of  Colombia 
this  great  mountain  system  is  crowned  with  hundreds  of  snow- 
capped peaks  and  studded  with  smoking  volcanoes.  For 
the  entire  distance  there  is  not  a  mountain  pass  or  gap  below 
12,000  feet  in  altitude,  while  the  loftiest  peaks  exceed  19,000 
feet,  —  Chimborazo,  20,498;  Cotopaxi,  19,613;  Antisana,  19,335; 
and  Cayambe,  19,186  feet. 

The  northern  portion  of  the  Andes  consists  of  three  or  four 
ranges  separated  by  deep  valleys  occupied  by  the  Magdalena 
River  and  its  tributaries,  which  drain  into  the  Caribbean  Sea.  The 
westernmost  range,  decreasing  in  height,  blends  with  the  Panama 
hills. 


THE  ATLANTIC    HIGHLANDS       •  IO9 

Very  important  in  its  bearing  upon  the  physical  geography  of 
the  continent  is  the  singular  proximity  of  the  Andes  to  the  west- 
ern coast.  Their  greatest  distance  from  it  scarcely  exceeds  100 
miles. 


Chimbokazo 
This  magnificent  Andean  peak  rising  above  the  valley  of  Quito  attains  the  height  of  20,498 

feet  above  the  sea. 

The  Atlantic  Highlands  of  South  America  are  those  of  Brazil 
and  Guiana. 

Th)e  Brazilian  Highland  is  a  broad  plateau  region  traversed 
by  nearly  parallel  ranges  of  moderate  elevation.  Their  loftiest 
peaks  are  from  5000  to  10,000  feet  high. 

Rising  above  the  sea  on  one  side  and  above  the  plains  on  the 
other  sides,  this  great  triangular  area,  embracing  700,000  square 
miles,  has  been  termed  the  "  Brazilian  Island." 

Its    drainage    is    mainly  inland,    to  the  Amazon    and    Plata 


no  RELIEF    FORMS   OF   NORTH    AND    SOUTH    AMERICA 

systems.  Only  one  important  river,  the  Sao  Francisco,  flows 
directly  into  the  Atlantic,  and  then  only  after  a  course  of  a  thou- 
sand miles  behind  mountain  barriers. 

The  Highland  of  Gniajia  is  a  plateau  supporting  several  closely 
set  ridges,  the  most  important  of  which  are  the  Parime  Mountains. 
Maravaca,  the  culminating  peak,  is  nearly  10,000  feet  high. 

The  Central  Region  of  South  America,  like  that  of  North 
America,  is  a  well-marked  depression  lying  between  the  superior 
and  inferior  highlands.  It  is  called  the  Great  Central  Plain.  It 
consists  of  the  river  basins  of  the  Orinoco,  the  Amazon,  and  the 
Plata.  These  are  divided  by  ridges  so  low  and  so  narrow  that 
the  three  together  may  not  unfairly  be  considered  as  formi  ig 
one  great  basin. 

The  following  curious  facts  will  show.how  nearly  alike  tlieir  level  actually 
is.  The  Cassiquiare.  which  rises  between  the  Amazon  and  the  Orinoco,  forks, 
after  running  some  distance,  and  sends  otf  one  l:)ranch  to  the  south  to  unite 
with  tiie  waters  of  the  Amazon,  the  other  to  unite  with  those  of  the  Orinoco 
on  the  north  :  it  thus  connects  these  two  river  basins  by  a  water  way  that 
permits  the  Indians  to  pass  in  their  canoes  from  either  of  the  two  great  rivers 
i.ito  the  other. 

P'urthermore.  in  the  Brazilian  province  of  Matto  (irosso  there  are  two 
springs  side  by  side,  and  within  a  few  feet  of  each  other.  From  one  the  water 
flows  into  the  Amazon,  from  the  other  into  the  Plata;  and  so  close  are  the 
navigable  waters  of  these  rivers  to  each  other,  that,  with  a  single  portage  of  a 
few  miles,  the  voyager,  ascending  the  Plata  from  the  sea,  may  return  to  ^•■'e 
ocean  again,  either  through  the  Amazon  or  the  -Orinoco. 

Silvas  of  the  Amazon. — The  valley  of  the  Amazon  is  not  only 
of  great  e.xtcnt,  but  it  is  very  level.  Lying  within  the  tropical 
rain  belt,  it  is  one  of  the  best  watered  regions  of  the  world.  This, 
together  with  the  warm  climate  and  rich  alluvial  soil,  has  been 
productive  of  remarkably  dense  forest  growths  known  as  silvas. 
So  close  together  are  the  trunks  of  the  trees  and  so  great  the 
tangle  of  vines  that  were  it  not  for  the  water  ways  this  region 
would  be  quite  impenetrable,  as  paths  are  cut  with  difficulty. 
During  the  rainy  seasons  the  lower  portions  of  the  valley  are 
flooded  far  and  wide  and  the  waters  even  flow  through  the  tree 
tops.     On  the  other  hand,  during  the  dry  seasons  the  waters  so 


LLANOS  I  1  1 

far  recede  as  to  leave  strips  of  meadow  land  exposed,  their  long 
submergence  having  effectually  checked  the  forest  growth. 

Llanos.  — West  of  the  Guiana  highland  the  low  valley  of  the 
Amazon  passes  imperceptibly  into  that  of  the  Orinoco,  and 
the  forest  growth,  so  characteristic  of  the  former,  soon  gives 
way  to  a  treeless  or  prairie  region.  During  the  wet  or  rainy 
season  these  plains  are  more  or  less  flooded,  but  later,  when 
the  water  recedes,  they  are  covered  with  a  luxuriant  growth  of 
coarse  grass  resembling  great  meadows,  hence  the  name  llanos 
which  has  been  applied  to  them.  During  the  dry  season,  how- 
ever, they  present  a  very  different  aspect :  The  Orinoco  no  longer 
fi\\s  its  banks,  but,  much  shrunken,  courses  its  way  seaward;  the 
grasses  and  other  vegetation  have  withered  away ;  the  once 
green  plains  have  taken  on  a  parched  and  desertlike  appear- 
ance ;  and  the  smaller  streams  have  ceased  to  flow. 

The  Chaco  and  Pampas.  —  The  third  of  the  great  South 
American  basins  is  that  of  the  Plata.  Lying  south  of  the 
Amazonian  basin,  it  is  separated  from  it  by  a  low  and  almost 
imperceptible  divide.  Its  northern  portion  is  wooded  and  in 
its  forests  and  swamps  are  found  both  wild  animals  and  In- 
dians. Famous  as  a  hunting  ground,  this  region  is  known  as 
The  Chaco.  Roughly  located,  it  lies  west  of  the  Paraguay  River 
and  north  of  the  Pilcomayo. 

The  larger  part  of  the  basin,  however,  is  in  the  form  of 
almost  level  plains,  although  occasionally  relieved  by  hills  and 
low  mountains.  They  are  the  pampas.  The  higher  plains 
vary  in  altitude  from  3000  to  600  or  700  feet.  They  are 
bordered  along  the  Plata  and  the  Parana  by  low  alluvial 
plains. 

The  pampas  vary  somewhat  in  their  surface  features.  In 
the  south  they  are  barren  and  sandy ;  north  and  west  of  the 
Cordoba  Hills  there  are  numerous  saline  basins,  and  in  the 
region  of  Buenos  Aires  there  are  rich  farming  lands.  Not- 
withstanding the  widespread  barrenness,  much  of  the  country 
is  covered  with  nutritious  grasses,  so  that  the  pampas  of  Argen- 
tina rank  among  the  greatest  a:razing:  lands  of  the  world. 


liM»^ 


^^ 


^ 


^  iJ         C 


.  ,:m^^s 


(112) 


V        I        A        Jf 


The  Red 


.«i 


Eurasia 


("3) 


XL     RELIEF    FORMS   OF    EUROPE,    ASIA, 
AFRICA,    AND    AUSTRALIA 

Europe,  like  North  and  South  America,  has  its  superior  and 
inferior  highlands  and  its  low  plain,  but  the  arrangement  of 
these  features  differs  from  that  prevailing  in  the  New  World 
in  two  well-marked  particulars :  ( i )  the  main  axis  of  elevation 
extends  east  and  west,  not  north  and  south,  as  in  the  case  of 
the  Rocky  Mountains  and  the  Andes;  (2)  the  mountain  chains 
do  not  exhibit  the  characteristic  parallelism  shown  by  those  of 
the  New  World. 

The  Superior  Highland  of  Europe  stretches  across  the  south- 
ern portion  of  the  grand  division,  from  the  Atlantic  to  the  Black 


Alps 


Profile  of  Europe  from  South  to  North 

Sea,  and,  if  we  regard  the  Caucasus  as  its  eastern  prolonga- 
tion, it  reaches  the  shores  of  the  Caspian. 

Beginning  with  the  Pyrenees,  its  western  termination,  it 
culminates  in  the  Alps.  Eastward  of  the  Alps  it  divides 
into  two  important  branches,  a  northern,  consisting  of  the  Car- 
pathian Mountains,  and  a  southern,  consisting  of  the  Dinaric 
Alps  and  the  Balkans.  These  ranges  inclose  the  Danube 
basin.  In  addition,  the  Apennines  of  Italy  and  the  moun- 
tains of  Greece  are  included  in  this  system. 

The  Alps,  which  cover  an  area  of  about  90,000  square  miles, 
are  the  most  celebrated  of  all  the  mountain  systems  in  the  world. 
Their  historic  and  poetical  associations,  the  grandeur  and  beauty 

114 


THE    ALPS 


115 


of  their  varied  scenery,  the  number  and  extent  of  their  <;laciers, 
and  their  accessibility  to  travelers  invest  them  with  an  interest 
unrivaled  by  the  loftiest  summits  of  other  lands. 

Occupying  a  central  position  between  France  and  Germany 
on  the  north,  and  Italy  on  the  south,  they  can  be  reached  in  a 
few  hours  from  any  of  the  great  cities  of  Europe.     Owing  to 


The  Jungfrau  from  Wengernali' 
This  snow-clad  Swiss  summit  is  a  most  imposing  sight.     Its  altitude  is  13,760  feet.      Dur- 
ing the  summer  months  avalanches  of  ice  are  of  common  occurrence,  falling  from  the 
heights  into  the  deep  valley  beyond  the  line  of  trees  in  the  foreground. 

their  varied  attractions  they  are  visited  by  so  many  thousands 
annually,  that  they  have  been  called,  not  inappropriately,  "  the 
playground  of  Europe." 

"  As  we  climb  the  Alps."  .says  a  distinguished  scientific  writer,  '"  peak  rises 
behind  peak,  crest  above  crest,  with  infinite  variety  of  outline,  and  with  a  wild 
grandeur  which  often  suggests  the  tossing  and  foaming  breakers  of  a  stormy 
ocean.  Over  all  the  scene,  if  the  air  be  calm,  there  broods  a  stillness  which 
makes  the  majesty  of  the  mountains  yet  more  impressive.     No  hum  of  bee  or 


Il6  RELIEF   FORMS   OF   EUROPE 

twitter  of  bird  is  heard  so  high.  No  brook  or  waterfall  exists  amid  those 
snowy  heights.  The  usual  sounds  of  the  lower  ground  have  ceased.  Now 
and  then  a  muttering  like  distant  thunder  may  be  caught,  as  some  loosened 
mass  of  snow  or  ice  falls  with  a  crash  into  the  valleys ;  or  the  wind  brings  up 
from  below  in  fitful  gusts  the  murmur  of  the  streams  which  wander  down  the 
distant  valleys." 

The  highest  peaks  of  the  Alpine  system  are  Mont  Blanc, 
15,730  feet;  Monte  Rosa,  15,217  feet;  and  the  Matterhorn, 
14,705  feet. 

The  Pyrenees,  which  extend  for  a  distance  of  about  250 miles 
from  the  Mediterranean  to  the  Bay  of  Biscay,  present  a  much 
greater  uniformity  of  arrangement  than  the  Alps.  Their  average 
height  (8000  feet)  is  not  greatly  inferior  to  that  of  the  Alps 
(8000  to  9000  feet);  but  their  highest  peak.  Mount  Maladetta, 
1 1,168  feet,  is  far  below  the  towering  masses  of  Mont  Blanc  and 
Monte  Rosa.  The  passes  of  the  Pyrenees,  however,  are  higher 
and  less  practicable  than  those  of  the  Alps. 

The  Carpathian  and  Balkan  Mountains. — The  Carpathians 
separate  the  plains  of  Hungary  from  the  great  low  plain  of 
Northern  Europe.     Their  greatest  elevation  is  about  9000  feet. 

Through  the  southwestern  extension  of  these  mountains,  known 
as  the  Transylvanian  Alps,  the  Danube  River  has  cut  a  long  and 
picturesque  passage  obstructed  by  numerous  rocky  ledges,  the 
chief  of  which,  the  Iron  Gate,  is  nearly  a  mile  in  width.  The 
former  dangers  to  navigation  at  this  point  have  been  removed 
by  the  construction  of  a  canal. 

South  of  the  Iron  Gate  the  mountain  barrier  merges  with  the 
Balkans,  which,  becoming  an  east-and-west  range,  is  terminated 
by  the  Black  Sea.  The  highest  summits  of  these  mountains  do 
not  exceed  7000  feet.  The  Dinaric  Alps  connect  the  Balkans 
with  the  Alps  proper. 

The  Caucasus  range  resembles  the  Pyrenees  in  that  it  lies  be- 
tween two  large  bodies  of  water,  the  Caspian  and  the  Black  seas, 
and  in  the  further  fact  that  it  is  well  defined.  On  the  north  are 
the  great  Russian  plains  and  on  the  south  the  river  Kur.  The 
length  of  these  mountains   is  about   700  miles  and  their  width 


PENINSULAS  1 1 7 

varies  between  70  and  120  miles.  Mount  Elburz(i8,526  feet), the 
most  conspicuous  peak,  exceeds  Mont  Blanc  in  height,  and  the 
entire  range  is  high,  with  a  snow-clad  crest  and  glaciers.  This 
great  mountain  barrier  forms  a  part  of  the  boundary  between 
Europe  and  Asia. 

Peninsulas.  —  High  Europe  throws  out  three  mountainous 
projections  toward  the  south  :  the  Iberian  or  Spanish  Peninsula 
on  the  west,  the  Italian  in  the  center,  and  the  Grecian  on  the 
east. 

The  Iberian  or  Spanish  Peninsula  is  a  great  plateau  surmounted  by  several 
parallel  ranges.  The  Pyrenees,  which  are  the  principal  of  these,  form  the 
dividing  line  between  France  and  Spain. 

In  the  Italian  Peninsula  we  find  the  Apennines,  an  important  prolongation 
of  the  Alpine  system.  These  are  more  famed  for  their  beauty  than  for  their 
altitude.  The  volcanoes  of  Vesuvius,  Etna,  and  the  Lipari  Islands  are  consid- 
ered as  belonging  to  this  chain. 

The  Grecian  Peninsula,  like  the  Italian,  boasts  of  no  very  elevated  ranges. 
Its  mountains  are  famed  less  for  their  height  than  for  their  historic  and  poetic 
associations.  They  were  the  mythic  homes  of  the  gods  of  ancient  Greece.  The 
throne  of  Jupiter  rested  on  Mount  Olympus. 

The  Inferior  Highlands  comprise  the  ranges  of  Scandinavia 
and  the  Ural  Mountains. 

The  Scandinavian  mountains  consist,  for  the  most  part,  of  a 
broadly  elevated  region  along  the  western  coast  of  the  penin- 
sula. Formerly  these  mountains  were  much  higher  than  now 
and  indented  by  many  deep  valleys.  By  subsidence  these  val- 
leys have  in  their  lower  portions  become  arms  of  the  sea  known 
as  fiords.  As  they  afford  safe  anchorage  and  often  extend  far 
inland,  sometimes  even  a  hundred  miles,  they  are  commercially 
of  great  value.  On  such  bodies  of  water  many  seaports  have 
been  established. 

The  Scandinavian  highlands  terminate  in  North  Cape,  a  great 
bluff,  nearly  a  thousand  feet  in  height,  facing  the  Arctic  Ocean. 
This  point  is  visited  annually  by  many  tourists  for  the  purpose 
of  beholding  the  "midnight  sun." 

The  Ural  Mountains  form  a  natural  boundary  between  Eu- 
rope and  Asia.     They  extend   southward,  along  the   meridian 


ii8 


KEl.lKF   FORMS   OF   KUROPE 


of  60°  east    1500  miles,  from  the  Arctic  Ocean  nearly  to  the 
Caspian  Sea. 

Low  Europe  consists  of  a  vast  plain  lying  northeast  of  the 
superior  highland.  It  is  bordered  on  the  northwest  by  the 
mountains  of   Scandinavia,  and  on  the  northeast  by  the   Ural 


North  Cape  from  the  West 

The  nortliern  end  of  tlie  Scandinavian  highlands. 

range.     It  extends  from  the  Arctic  Ocean  to  the  Black  Sea, 
and  westward  as  far  as  the  Bay  of  Biscay. 

The  Valdai  Hills,  having  an  altitude  of  about  a  thousand  feet, 
mark  the  highest  point  of  a  swell  which  separates  the  rivers 
flowing  into  the  Baltic  and  White  seas  from  those  which  enter 
the  Black  and  Caspian. 


THK    SUPEKIUK    HKiHLAND    OK   ASIA  1 19 

The  range  of  this  plain  in  latitude  is  so  great  and,  as  a  direct  consequence, 
its  climate  so  varied,  that  it  presents  several  well-marked  aspects.  The 
northern  portion  is  treeless  and  of  tlie  general  character  of  the  lands  border- 
ing the  Arctic  coasts  in  both  hemispheres.  Farther  south  forest  lands  appear, 
which  still  farther  south  give  way  to  rich  prairie  lands  excepting  in  regions 
bordering  the  Caspian,  where  saline  conditions  prevail. 

The  Superior  Highland  of  Asia  consists  of  two  portions : 
( I )  the  various  mountain  chains  which  radiate  from  the  central 
elevated  region  known  as  the  plateau  of  Pamir;  and  (2)  the 
plateau  of  Tibet. 

The  Pamir  is  called  by  the  Asiatics  the  "roof  of  the  world." 
In  shape  it  may  be  regarded  as  an  irregular  square.  From 
three  of  its  corners  great  chains  project.  The  southeast  corner 
is  the  starting  point  of  the  great  ridges  of  the  Himalaya,  the 
Karakoram,  and  Kuen-Lun.  From  the  northeastern  corner  the 
Thian  Shan  range  takes  its  origin.  From  the  southwestern 
starts  the  line  of  the  Hindu  Kush. 

The  plateau  of  Tibet  lies  between  the  Himalayas  on  the 
south  and  the  Kuen-Lun  Mountains  on  the  north.  It  is  the 
loftiest  table-land  in  the  ivorld,  having  an  extreme  elevation  of 
about  15,000  feet. 


30000 

HIMALAYA     MTS. 

.i* 

25000 
20000 
15000 
10000 

i^ 

J~          THIAN  SMAN 
^                   /I  MTS. 

5000 

.jJiJ^mW 

ua^ 

^^ 

SIBERIAN         PLAIN 


Fkomi.e  ()!•  .Asia  ikdm  .soi  i  a   10  NOriu 

The  Himalayan  Range  stretches  eastward  from  the  Pamir  in 
an  unbroken  course  for  a  distance  of  1500  miles.  Its  breadth 
varies  from  150  to  350  miles,  and  its  mean  height  has  been  esti- 
mated at  6000  feet  higher  than  that  of  the  Andes.  Over  40 
of  its  peaks  rise  to  an  altitude  of  23,000  feet,  and  more  than 
70  reach  20,000  feet.  Mount  Everest,  with  an  elevation  of 
29,000  feet,  is,  so  far  as  known,  the  highest  mountain  on  the 
globe. 


I20  RELIEF   FORMS  OF   ASIA 

The  Himalayas  present  the  grandest  possible  mountain  scenery ;  deep 
gorges  wrapt  in  perpetual  twilight  gloom ;  frightful  precipices  ;  somber  for- 
ests of  rhododendrons  and  pine  trees ;  higher  up,  vast  glaciers  filling  the 
ravines,  and  ice  and  snow  covering  the  ridges  which  rise  one  above  another 
to  such  sublime  heights  as  must  ever  secure  their  summits  immaculate  from 
the  footsteps  of  man.  Everything  is  colossal ;  but  the  Himalayas  lack  the 
smiling  valleys  and  sheltered  lakes  which  impart  such  picturesque  charm  to 
the  Alps.  They  possess  the  grandeur  without  the  amenity,  the  magnificence 
without  the  variety,  which  mark  the  less  elevated  European  system. 

The  passes  of  the  Himalayas,  instead  of  leading  through  low  gaps  and 
over  gentle  declivities,  rise  up  into  the  regions  of  perpetual  snow  and  ice, 
and  are  so  difficult  as  to  be  of  little  avail  for  the  purposes  of  commerce  be- 
tween the  people  on  the  opposite  sides.  They  are  on  an  average  10,000  feet 
higher  than  those  of  the  Alps,  and  nearly  4000  feet  higher  than  those  of  the 
Andes.  We  cannot  be  surprised  that  India  and  Siberia  are  practically  farther 
removed  from  each  other  than  if  they  were  separated  by  an  ocean,  nor  even 
that  the  opposite  slopes  of  the  Himalayas  are  occupied  by  men  of  different 
races. 

The  Karakoram,  Kuen-Lun,  and  Thian  Shan  Mountains. — The 

Karakoram  range  traverses  the  plateau  of  Tibet,  and  is  supposed 
to  have  a  greater  average  height  than  even  the  Himalayas.  It 
contains  Mount  God  win- Austen  (height,  28,278  feet),  believed  to 
be  the  highest  summit  next  to  Mount  Everest  in  the  v^^orld. 

The  Kuen-Lun  range  separates  Tibet  and  eastern  Turkestan, 
and  is  prolonged  by  the  Chinese  range  of  the  Pe-Ling. 

The  Thian  Shan  range  forms  the  northern  boundary  of  the 
plateau  of  eastern  Turkestan.  Some  of  its  peaks  attain  the 
height  of  20,000  feet. 

The  Hindu  Kush  extends  in  broad,  massive  ranges  westward 
for  400  or  500  miles.  A  depression  then  occurs.  The  range, 
however,  is  really  continued  in  the  Elburz  Mountains,  which 
form  the  northern  boundary  of  Persia. 

The  general  direction  of  the  great  mountain  chains  of  the 
superior  highland  region  is  east  and  west. 

The  Inferior  Highlands  comprise  the  Altai  Mountains  and 
their  northeastern  continuations,  together  with  the  Great  Khin- 
Gan  range,  and  the  ranges  of  southeastern  Asia,  and,  finally, 
the  subordinate  plateaus  of  the  grand  division. 


THE  ALTAI   AND   THE   KHIN-GAN   MOUNTAINS  121 

The  Altai  and  the  Khin-Gan  Mountains.  —  The  Altai  Moun- 
tains, extending  in  a  northeasterly  direction,  are  continued  in 
the  Yablonoi  and  Stanovoi  ranges.  They  separate  the  desert 
wastes  of  Mongolia  from  the  plains  of  Siberia.  Some  of  their 
peaks  are  12,000  feet  high. 

"Although  far  less  extensive  and  elevated  than  the  Thian  Shan,  the  Altai 
still  bears  comparison  with  the  European  Alps,  if  not  in  the  height  of  its  peaks, 
diversity  of  its  forms,  abundance  of  its  snow  or  rich  vegetation,  at  least  in  the 
development  of  its  ranges  and  the  length  of  its  valleys."  —  Reclus. 

The  Khin-Gan  Mountains,  with  their  southern  offshoots,  form 
the  eastern  barrier  of  the  great  Desert  of  Gobi. 

The  Plateaus  of  Asia  are  a  prominent  feature  of  the  grand  divi- 
sion. They  extend  in  a  series  from  the  shores  of  the  Red  Sea 
nearly  to  the  Pacific  Ocean.  In  general  they  are  arid  and  rainless, 
sandy,  stony,  and  barren.  In  the  spring  their  surface  is  thinly 
sprinkled  here  and  there  with  grass  and  herbs,  but  in  the  sum- 
mer and  autumn  it  is,  for  the  most  part,  dry  and  sterile. 

The  sheltered  valleys  are,  however,  in  many  cases  exceed- 
ingly fertile.  In  such  valleys  there  is  a  settled  population,  but 
outside  of  them  the  plateau  region  may  be  described  as  the 
home  of  roving  herdsmen  and  marauding  Bedouin. 

North  of  the  Kuen-Lun  Mountains  are  two  plateaus,  eastern  Turkestan  and 
the  Desert  of  Gobi.  These  are  shut  in  on  the  north  by  the  Thian  Shan  and 
Altai  Mountains.  The  average  elevation  of  eastern  Turkestan  is  about  2000 
feet  above  the  sea  level ;  that  of  Gobi,  about  4000  feet.  Entering  Gobi  from 
Tibet,  we  should  descend  fully  9000  feet. 

The  triangular  plateau  of  the  Dekkan  in  India  rises  to  the  average  height 
of  about  3000  feet.  The  sides  of  the  triangle  are  the  eastern  Ghats,  the 
western  Ghats,  and  on  the  north  the  Vindhya  Mountains. 

The  plateau  of  Iran  or  Persia,  including  large  portions  of  Afghanistan  and 
Baluchistan,  is  shut  in  by  the  Elburz  and  Hindu  Kush  Mountains  on  the  north, 
by  the  Zagros  chain  on  the  south,  and  the  Sulaiman  on  the  east.  It  rises  from 
3000  to  4000  feet  above  the  sea  level. 

The  plateau  of  Armenia,  with  Ararat  (about  17,160  feet  high)  for  its  culmin- 
ating point,  rises  to  the  westward  of  Persia. 

The  plateau  of  Asia  Minor  lies  westward  of  that  of  Armenia.  It  has  an 
average  elevation  of  2500  feet.     The  Taurus  ranges  bound  it  on  the  south. 

The  plateau  of  Arabia  forms  the  southwestern  projection  of  Asia. 


122 


RELIEF   FORMS   OF  ASIA 


The  Great  Lowland  of  Asia  lies  to  the  north.  It  extends 
from  the  shores  of  the  Arctic  Ocean  southward  to  the  base  of 
the  Altai  Mountains  and  the  adjacent  ranges,  and  comprises  the 
Kirghiz  Steppes  and  the  Siberian  Plain. 

It  is  a  part  of  the  almost  continuous  depression  which  extends  through 
I-'urope  and  Asia,  from  the  North  Sea  to  Bering  Strait,  a  distance  of  more 
than  5000  miles. 

The  Kirghiz  Steppes  are  wide  and  monotonous  tracts,  covered 
in  spring  with  rough  grass,  parched  with  drought  in  summer, 
and  bleak  and  desolate  in  winter. 


The  Dead  Sea,  Paeestink 
This  remarkable  salt-water  lake  occupies  the  deepest  known  depression  of  the  land  below 
sea  level.  Its  length  is  47  miles;  its  greatest  width  does  not  exceed  10  miles;  its  sur- 
face is  1292  feet  below  that  of  the  Mediterranean  Sea ;  and  its  greatest  depth  is  1310 
feet.  From  the  eastern  and  western  margins  of  the  sea  the  land  rises  precipitously 
in  the  form  of  great  limestone  cliffs. 

The  Siberian  Plain  consists  of  prairies  and  piny  forests  in  its 
southern  portions;  of  swanipy  tundras  on  its  northern  edges. 


m\ 


the:  grand  division  of  africa  123 

Inferior  in  size  to  the  Siberian  Plain,  but  vastly  more  impor- 
tant for  their  influence  upon  the  history  of  the  human  race,  are 
the  plains  of  China  and  India.  They  support  nearly  one  half 
the  population  of  the  globe. 

Two  remarkable  depressions  are  found  on  this  grand  division. 
One  is  occupied  by  the  Dead  Sea,  the  surface  of  which  is  1292 
feet  below  the  level  of  the  ocean  ;  the  other  by  the  Caspian,  the 
surface  of  which  is  84  feet  below. 

The  Grand  Division  of  Africa  obeys  less  closely  the  general 
law  of  continental  relief.  It  has,  however,  mountain  ranges  along 
the  coast,  while  a  plateau  region  of  less  elevation  occupies  the 
interior.  Its  superior  highland,  lying  on  the  east,  is  broken  by 
rivers  into  pronounced  segments.  Notwithstanding  that  its 
mean  elevation  is  said  to  exceed  that  of  Europe  and  even  Asia, 
its  mountains  can  scarcely  be  compared  with  the  Alps  in  magni- 
tude, much  less  with  the  Himalayas. 

The  Superior  Highland  consists  of  an  elevated  region  which 
extends  from  the  Isthmus  of  Suez  to  the  Cape  of  Good  Hope. 
One  important  portion  of  it,  the  plateau  of  Abyssinia,  attains 
an  elevation  of  7000  to  8000  feet.  The  culminating  points, 
however,  are  the  snowy  heights  of  Kenia,  Kilimanjaro,  and  the 
Ruwenzori  Mountains  (about  19,000  feet),  near  the  equator. 
South  of  these  elevations  occur  the  Livingstone  Mountains 
(5000  to  10,000  feet),  walling  in  Lake  Nyassa;  and  nearly  at  the 
southern  extremity  of  the  continent  lie  the  Snow  Mountains, 
which  may  be  considered  as  vast  terraces  ascending  from  the 
sea  toward  the  interior. 

The  plateau  of  Abyssinia  has  been  described  as  a  '•  block  "  of  the  older 
crystalline  rocks,  gneisses,  and  scliists.  capped  with  lava  sheets.  Its  surface 
has  been  profoundly  eroded,  and  in  places  the  accumulation  of  volcanic  matter 
is  said  to  form  high  mountains.  Lake  Deml^ea  occupies  a  depre.ssion  3000 
feet  below  the  general  level  and  is  regarded  as  the  chief  source  of  the  Blue 
Nile. 

The  Inferior  Highlands  include  the  ranges  which  border  the 
northern  and  western  coasts.  The  Atlas  Mountains  on  the 
north  consist  of  three  or  four  parallel  ranges  which  ascend  from 


124 


RELIEF  FORMS  OF  AFRICA 


The  Relief  of  Africa 

the  Mediterranean  stage  by  stage,  and  increase  in  height  to  the 
westward. 

The  Kameruns  and  the  mountains  near  the  headwaters  of  the 
Niger  are  the  principal  elevations  on  the  west.  The  Kameruns 
are  volcanic.  They  attain  at  some  points  the  height  of  nearly 
13,000  feet. 


THE    IMKKIOR 


125 


The  Interior  of  the  i;rancl  division  may  be  regarded  as  a  vast 
plateau  bordered  by  the  various  coast  ranges.  Low  plains  are 
to  be  found  onh'  along  the  coast. 


I^f%  /[ 

\ 

^ 

In 
-^  1 9 1 

-■mtf^^^^^^j        -A-"^-^^^ 

M 

^ 

A    CAKAVAiN    UN     IHE    DESKRT   OF   SAHAK.\ 

The  plateau  region  may  be  divided  into  two  sections:  (i) 
that  portion  which  consists  of  prairies  and  fertile  river  basins  ; 
and  (2)  the  arid  Sahara. 

The  Sahara  stretches  east  and  west  3000  miles,  north  and  south 


ijCENE  UN   THE   DtaKRl    OF   SaUAKA 


1000,  covering  an  area  of  2^  millions  of  square  miles.  It  is  not 
an  absolute  level.  Its  average  elevation  is  about  1200  feet,  but 
it  contains  areas  which  are  4000  or  5000  feet  in  height,  and 
has  a  mountain    range  one  of  whose  peaks  is  nearly  8000  feet 


126 


RELIEF   FORMS   OF   AUSTRALIA 


The  Relief  of  Australia 


high.  Southward  of  Tunis  are  found  depressions,  some  of 
which  are  lOO  feet  below  sea  level.  They  are  marshy  regions 
for  most  of  the  year,  but  when  the  winter  rains  fall  they  receive 
the  drainage  from  the  mountains,  and  thus  become  broad,  open 
lakes  known  as  chottes  {shots).  The  surface  of  the  desert  con- 
sists, in  some  places,  of  sharp  stones,  in  others  of  gravel,  in 
others  again  of  shifting  sand.  »The  latter  when  driven  before 
the  wind  is  arranged  in  long,  huge  billows  called  dimes. 

Here  and  there  over  the  desert  are  found  fertile  spots  or  oases 
where  water  may  be  obtained  either  from  springs  or  wells. 

Australia  somewhat  resembles  Africa  in  its  relief.  It  has  an 
elevated  border  and  a  depressed  interior. 

The  superior  highland  lies  along  the  eastern  and  southeastern 
shores.     It  includes  the   Blue  Mountains    and    the    Australian 


AUSTRALIA  127 

Alps,  culminating  in  the  latter,  the  loftiest  peaks  of  which  are 
about  7000  feet  high. 


Inspiration  I'oim,  Bi.i  k  Moumain.s,  New  Soiin  Wales,  Aisikaeia 
Photographed  by  Sterling  R.  Fulmore. 

The  inferior  highland  borders  the  western  and  northwestern 
portions  of  the  continent. 

Of  the  central  lowland  the  basins  of  the  Darling  and  Murray 
rivers  are  best  known.  Of  the  remainder  much  is  desertlike. 
A  characteristic  feature  of  the  lowland  is  its  inland  salt  lakes, 
which  cover  large  areas  during  the  rainy  season,  but  shrink  to 
saline  marshes  or  completely  disappear  during  the  dry  season. 


SIAI£  RORMAL  SCMOOi, 

UOS  AKGEUES,  CRlt. 


M.-S.  I'HYS.  GEOG.  ■ 


XII.    ISLANDS 


Classification.  —  As  distinguished  from  continents  the  smaller 
land  masses  rising  above  the"  sea  are  termed  islands.  They 
vary  greatly  in  size,  from  the  mere  protrusion  of  a  rocky  or 
low-lying  mud  or  sand  bank,  a  few  square  feet  in  area,  to  land 

masses  hundreds  of 
square  miles  in  ex- 
tent, which,  in  their 
general  character- 
istics, are  not  unlike 
the  continents  them- 
selves. 

According  to  their 
origin  and  structure 
islands  may  be  classi- 
fied into  two  groups : 

( 1 )  continental; 

(2)  oceanic. 
Continental  Islands, 

as  their  name  im- 
plies, rise  from  the 
submerged  continen- 
tal borders  and  not 
from  the  deeper  parts 
of  the  ocean's  floor. 
At  earlier  periods  in 
the  earth's  history 
many  of  them  were 
actually  parts  of  the 
continents  from  which  they  have  been  separated  by  setthng 
(subsidence),  wave  wear  (erosion),  or  a  combination  of  both. 

128 


The  British  Islands  and  the  Submarine  Plat- 
form ON  WHICH  THEY  REST.     After  Geikie. 
The  tinted  area  is  less  than  100  fathoms  in  depth. 


OCEANIC  ISLANDS 


129 


Sea  exploration  and  soundings  show  that  the  British  Islands  rest  upon  a 
submarine  platform  which  cannot  be  regardeid  as  other  than  an  extension  of 
the  mainland  of  Europe.     This,  together  with  their  geologic  structure,  goes 
to  show  their  intimate  re- 
lation to  the  existing  con- 
tinent, of  which,  in  fact, 
they  form  a  part. 

Other  coastal 
islands  have  resulted 
from  the  cotistriictive 
action  of  the  waves 
by  which  mud  banks, 
sand  spits,  and  reefs 
have  been  thrown  up. 
Once  above  the  water, 
their  growth  is  aided 
by  the  springing  up 
of  coarse  grasses  and 
other  forms  of  vege- 
tation which  gradually 
collect  and  hold  in 
place  additional 
matter. 

Along  the  Gulf  coast 
of  Texas  long  barrier  is- 
lands, broken  by  occa- 
sional inlets,  have  been 
built  up  by  the  waves 
driven  shoreward  by  the 
prevailing  winds.  The 
filling  up  of  shallow 
sounds  and  the  present  growth  of  islands  is  also  well  illustrated  along  the 
coast  of  North  Carolina. 


Map  OP'  THE  Coastal  Portion  of  North  Carolina 

In  this  partially  drowned  region  the  outer  sand  reefs,  in 
the  form  of  long,  narrow  islands,  almost  completely 
close  the  entrances  to  Albemarle  and  Pamlico  sounds. 
The  inclosed  bodies  of  water  are  being  gradually  filled 
by  the  silt  and  sand  brought  from  the  land  by  river 
action. 


Oceanic  Islands  are  situated  far  from  the  continents.  They 
rise  from  the  deeper  portions  of  the  ocean's  floor.  In  structure 
they  are  strikingly  unlike  most  continental  islands,  being  either 
volcanic  or  coralline.     The  former  often  rise  thousands  of  feet 


130 


ISLANDS 


above  the  sea  level,  while  the  latter  are  low-lying  and  devoid  of 
surface  relief. 

Oceanic  islands  of  the  first  group  are  the  tops  of  volcanic 
peaks  which  rise  above  the  sea  through  their  own  upbuilding ; 
the  islands  of  the  second  group  are  brought  to  the  surface  by 

the  upbuilding  of 
coral  reefs  from  high 
submarine  volcanic  or 
other  platforms. 

Volcanic  Islands  are 
arranged,  as  a  rule, 
along  the  great  bands 
or  belts  of  volcanic 
activity  which  trav- 
erse the  globe. 

Most  of  them  are 
found  within  the  vol- 
canic belts  of  the 
Pacific  and  the 
Atlantic.  There  are, 
however,  exceptions 
to  this  general  rule, 
many  volcanic  islands 
being  situated  quite 
irregularly.  The  volcanoes  upon  islands  in  the  Pacific  belt  are 
among  the  most  active  in  the  world  ;  those  in  the  Atlantic  belt 
are  far  less  active,  and  many  are  either  extinct  or  bordering  on 
extinction. 

Volcanic  islands  are  formed  by  the  accumulation  of  materials 
thrown  out  by  submarine  volcanoes.  Sometimes  such  islands 
are  formed  very  suddenly,  as  in  the  case  of  Graham  Island,  in 
1831,  and  that  off  the  island  of  Santorini,  in  the  Mediterranean, 
in  1866. 

Coral  Islands  are  found  especially  in  the  southern  Pacific  and 
Indian  oceans.  They  are  a  result  of  coral  growth  and  wave 
action.      The    coral  animal    is    -a.  polyp  —  not  an   in.scct,  but  an 


Brain  Coral 
In  this  figure  there  is  shown  a  coral  skeleton,  that  is, 
"dead  coral,"  which  is  composed  of  carbonate  of 
lime,  the  substance  of  limestone.  The  living  portions 
of  coral,  the  polyps,  are  soft  and  fragile,  and  when 
removed  from  the  sea  water  soon  dry  up  and  disappear. 


(t>KAl,    ISLANDS  131 

animal  imich  lower  in  the  scale  oi  lile  —  which  secretes  from 
sea  water  a  skeleton  composed  of  carbonate  of  lime,  the  sub- 
stance of  limestone.  Many  polyps  are  usually  supported  in 
common  by  a  single  skeleton,  which  may  be  of  a  delicate 
branching'  form  or  a  great  rounded  mass  or  head.  Begin- 
ning" in  water  not  exceeding  20  fathoms,  more  often  6  or  7 
fathoms,  the  reef-building  coral  by  the  growth  and  accumu- 
lation oi  its  hard  parts  lays  the  foundation  of  what  may  be- 
come a  reef  or  a  coral  island.  In  all  cases  this  coral  growth 
rises  from  a  submarine  platform  which  not  infrequently  is  the 
submerged  summit  of  a  volcanic  peak.  Polyps  thrive  best  when 
immersed  in  pure  sea  water;  accordingly  they  exhibit  the 
greatest  profusion  on  the  exterior  or  seaward  side  of  a  reef. 
As  they  approach  the  surface,  the  finer  and  more  delicate 
skeletons  are  broken  by  the  dashing  of  the  waves,  and  their 
fragments,  settling  down  among  larger  coral  heads,  fill  the 
interstices  and  serve  eventually  to  cement  and  solidify  the  reef. 
Finallv  the  level  of  low  tide  is  reached  and  the  upward  growth 
of  the  polyps  is  checked. 

The  further  upbuilding  of  the  reef  now  becomes  the  work  of 
the  waves  —  a  v^^ork  of  destruction  and  of  construction.  Portions 
of  coral  growth  are  torn  from  their  beds,  broken  up,  ground  as 
sand  on  a  beach,  and  swept  into  a  long  ridge. 

The  ridge,  heaped  up  by  successive  additions  of  broken  coral, 
finally  becomes  so  high  that  it  overtops  the  waves,  and  an  island 
is  formed. 

The  next  stage  is  the  appearance  of  vegetable  life.  Floating 
wood  lodges  among  the  coral  fragments.  It  decays  and  forms 
mold.  Seeds,  such  as  cocoanuts,  not  injured  by  salt  water,  are 
wafted  to  the  newly  formed  islet ;  others  may  be  carried  thither 
by  birds.  Under  the  stimulus  of  a  tropical  sun  they  grow,  and 
in  time  cover  the  dead  coral  mass  with  living  green. 

The  breadfruit  and  cocoa  palm  are  the  most  important  of  the 
forms  of  plant  life  that  flourish  upon  such  islands.  No  large 
animals  live  upon  them,  and,  on  account  of  their  small  areas, 
they  can  sustain  only  a  limited  population. 


132 


ISLANDS 


Coral  Reefs  may  be  classed  as  (i)  fringing  reefs;  (2)  barrier 
reefs;  (3)  atolls. 

Fringing  reefs  occur  near  the  shore  line  surrounding  islands  or 
skirting  the  coasts  of  continents.  Many  Pacific  islands  furnish 
examples  of  such  reefs,  as  well  as  the  eastern  coasts  of  Africa 
and  South  America  within  the  equatorial  belt. 

Barrier  reefs  are  quite  like  fringing  reefs,  but  farther  removed 
from  the  land.     They  represent  a  later  stage  of  reef  develop- 


Atoll 


ment  when,  by  the  action  of  the  waves  and  the  growth  of  coral, 
the  reef  formation  has  advanced  seaward.  In  the  meantime  the 
inner  side  of  the  reef  has  been  slowly  dissolving  away,  leaving 
an  ever-increasing  interval  of  shallow  water  between  it  and  the 
land.  In  some  instances  it  is  possible  that  fringing  reefs  may 
have  been  transformed  into  barrier  reefs  by  the  gradual  subsid- 
ence of  the  sea  bottom,  whereby  the  reef,  growing  upward  to 
the  surface,  appears  at  a  considerable  distance  from  the  shore. 
This  is  illustrated  by  the  diagrams  on  page  133. 

The  great  barrier  reef  off  the  northeast  coast  of  Australia  is  1250  miles  long 
and  from  10  to  90  miles  wide.  The  island  of  New  Caledonia  and  many  others 
are  protected  from  the  sea  by  similar  reefs. 

An  atoll  vs,  a  belt  or  strip  of  coral  reef  inclosing  an  expanse  of 
water  called  a  lagoon. 


ORIGIN  OF  ATOLLS 


133 


Diagrammatic 
Formation 
Atoll 


Illustrations    of 
OF  Barrier  Reek 


THE 

AND 


Atolls  are  usually  nearly  ov'al  or  circular,  but  in  many  cases 
they  are  quite  irregular  in  shape.  Sometimes,  as  in  the  case  of 
Whitsunday  Island,  they  are  complete  rings;  but  most  frequently 
on  the  side  not  exposed  to 
the  prevailing  winds  there 
are  one  or  more  breaks,  form- 
ing inlets. 

The  atolls  are  almost  innumer- 
able. There  are  nearly  a  hundred 
of  them  in  the  Dangerous  Archi- 
pelago, which  lies  to  the  westward 
of  Tahiti.  Thev  are  not  more  than 
half  a  mile  across,  from  the  sea  to 
the  lagoon.  In  their  highest  parts 
they  are  only  a  few  feet  above  the 
water;  still,  they  resist  the  utmost 
fury  of  the  waves.  They  are  thickly 
covered  with  vegetation. 


Section  of  mountain  rising  above 
water,  forming  an  island ;  RR,  section 
of  fringing  reef  resting  on  slopes ; 
A,  height  of  sea  level  as  shown  in  II 
below ;  B,  height  of  sea  level  as  shown 
in  III  below. 

II 


Origin  of  Atolls.  —  Many 
of  the  reefs  and  atolls  rise 
from  very  great  depths ;  but 
the  polyps  are  most  vigorous 
in  water  not  deeper  than  60 
feet ;  and  in  water  that  is 
more  than  150  feet  deep 
they  cease  to  live.  The  ques- 
tion, therefore,  arises,  how 
can  the  foundations  have  been 
laid    for    certain    reefs    and 

atolls,  which  stand  in  water  not  less  than  a  mile  and 
deep .'' 

Darwin  suggested  an  answer  which  enables  us  to  understand 
not  only  how  atolls  in  deep  water  may  have  originated,  but  also 
how  atolls  in  general  have  been  formed.  It  is  well  known  to 
geologists  that  the  level  of  the  ocean  bed  is  subject  to  change. 
It  may  be  upheaved,  or,  again,  it  may  subside.  Darwin  conjec- 
tured that  as   fast  as  the  coral  reef  was  built  up  toward  the 


L,  section  of  mountain  rising  above  water 
after  partial  submergence ;  RR,  sections 
of  barrier  reef  resting  on  slopes. 


Ill 


L,  section  of  same  mountain  after  complete 
submergence ;  RR,  sections  of  same 
reef  now  forming  an  atoll. 


half 


134  ISLANDS 

surface,  it  was    carried   down  by  the  subsidence  of  the  ocean 

bed. 

Let  us  notice  the  successive  steps  of  this  process.     There  is 

reason  to  beHeve  that  in  those  parts  of  the  ocean  where  atolls 

now  abound,  high  mountains  once  towered.     These  mountains 

were  islands.     The  polyps   built  encircling  reefs  around  them. 

But  in  many  cases,  as  they  built  up,  a  gradual  subsidence  took 

place,   until   the  islands  them- 

s'  selves  disappeared  beneath  the 

'---.,     ^    ..•  ■  ■  waves.      This    subsidence,    on 

the  one  hand,  and  this  building 

up,    on    the    other,    may    have 

continued  for  ages,  and  to  the 

extent  of  thousands  of  feet,  so 
Theoretical  Section  of  an  Atoll  ' 

RR,  reef;  6-.  summit  of  island;   6',   former    that  where  the  mountains  then 

summit  of  island.  were,  there  may  now  be  deep 

waters  and  low  atolls.  Thus 
the  mountain  tops  were  replaced  by  the  lagoons,  and  the  en- 
circling reefs  became  coral  islands. 

Tahiti  affords  an  illtistration  of  tiiis  process.  It  is  a  volcanic  island  witli  a 
fringing  reef,  the  foundations  of  wiiich  rest  upon  the  submarine  slopes  of  the 
Lsland.  It  exhibits  the  appearance  which  must  have  been  presented  by  existing 
atolls  before  the  subsidence  of  the  ocean  floor  had  carried  down  beneath  the 
surface  of  the  sea  the  mountainous  islands  formerly  inclosed  by  them. 

Other  views,  however,  have  been  advanced,  among  them  those 
of  Sir  John  Murray  of  the  Challenger  Expedition,  showing  that 
in  the  explanation  of  the  origin  of  barrier  re.efs  and  atolls  sub- 
sidence IS  not  necessary. 

Through  wave,  action  any  summit  rising  above  the  sea  may  be 
leveled  so  as  to  form  a  submarine  platform  upon  which  a  reef 
may  secure  a  foundation.  If  the  eminence,  usually  a  volcanic 
peak,  is  not  completely  leveled,  there  remains  an  island  sur- 
rounded by  a  barrier  reef.  This  reef  is  all  the  time  broadening 
its  foundation  by  the  addition  of  its  own  waste  and  thus  pushing 
outward  into  the  deeper  water.  Should  it  take  on  an  annular 
form,  inclosing  a  lagoon,  with  or  without  an   island,  it  forms  an 


DlSlKIBUriON    Oh    Ci)RAL  I  35 

atoll.  Such  a  coral  island  has  resulted  from  simple  reef  building 
without  subsidence.  Murray  entertains  the  view  also  that  the 
lagoon  may  be  deepened  b\  the  solvent  action  of  sea  water  upon 
the  dead  coral. 

Distribution  of  Coral. — The  reef-building  polyps  are  con- 
fined to  tropical  waters  which  have  a  temperature  of  not  less 
than  68°.  The  central  part  of  the  Pacific  Ocean  is  the  scene  of 
their  greatest  activity.  They  are  also  found  in  many  portions 
of  the  Indian  Ocean,  in  the  Red  Sea,  and  the  Persian  Gulf. 

Except  among  the  West  Indies,  at  the  Bermudas,  and  off  the 
coast  of  Brazil,  there  are  none  in  the  Atlantic. 

The  area  within  which  they  are  at  work  is  not  less  than  25 
millions  of  square  miles. 


PART    III.— THE    WATER 

XIII.     PROPERTIES   OF   WATER 

Composition  and  Properties  of  Water.  —  Pure  water  is  composed 
of  two  gases,  oxygen  and  hydrogen,  united  in  the  proportion  of 
one  volume  of  the  former  to  two  volumes  of  the  latter.  It  is 
represented  by  the  chemical  symbol  HgO. 

Among  the  properties  of  water  that  especially  interest  the 
geographer  are  the  following : 

(i)    It  changes  its  forms  with  remarkable  readiness  ; 

(2)  it  expands  when  passing  into  the  solid  state  ; 

(3)  it  has  great  capacity  for  absorbing  heat ; 

(4)  it  has  great  solvent  power. 

Forms  of  Water.  —  Water  exists  in  three  forms  or  states  :  the 
solid,  the  liquid,  and  the  gaseous.  Changes  of  temperature  of 
ordinary  occurrence  cause  it  to  pass  from  one  to  another  of 
these.  As  a  solid  it  may  fall  gently  as  snow,  muffling  the  young 
plants  and  screening  them  from  the  biting  winds  of  winter,  or 
as  ice  it  may  cover  the  surface  of  lakes  and  rivers,  protecting 
aquatic  forms  of  life  as  snow  does  the  plants  and  insects  of  the 
land.  As  a  vapor  it  passes  off  from  the  surface  of  the  seas, 
lakes,  and  rivers,  and  even  from  the  land  itself,  into  the  atmos- 
phere. Mantling  the  earth  with  an  invisible  screen,  it  prevents 
the  too  rapid  escape  of  its  warmth  at  one  time  ;  or,  assuming 
the  form  of  clouds  in  the  sky,  shields  it  from  the  too  great  heat 
of  the  sun  at  another,  and  when  still  further  condensed  it  falls 
as  rain,  supplying  water  to  springs  and  rivers  and  necessary 
moisture  to  animals  and  plants. 

Expansion  of  Water.  — Water  expands  when  passing  from  the 
liquid  state  to  the  solid.  This  is  probably  due  to  the  fact  that 
its  particles,  when  crystallized,  do  not  fit  so  closely  together  as 

136 


J 


CAPACITY   OF   WATER   FOR   ABSORBING    HEAl'  137 

before.  When  cooled,  it  follows  the  general  law,  and  contracts 
until  it  reaches  the  temperature  of  39.2°  F.  Below  this  it  disobeys 
the  general  law,  and  expands  till  it  reaches  32°,  its  freezing 
point.  Then  suddenly  it  hardens  into  ice,  and  attains  its  maxi- 
mum expansion. 

Since  ice  is  more  expanded  than  water,  it  is  lighter  than  water, 
and,  as  we  all  know,  floats.  Were  ice  heavier  than  water,  it 
would  sink  as  fast  as  it  was  formed,  and  our  river  channels  and 
shallow  lakes  would  be  filled  with  solid  ice  from  the  bottom  to 
the  top. 

Another  important  consequence  of  the  expansion  of  water 
when  freezing  is  that  it  exerts  a  force  that  is  practically  irresist- 
ible. It  sunders  the  solid  rock  from  the  foundations  of  the 
mountains,  and  crumbles  it  into  fragments. 

Interesting  examples  of  the  effects  of  the  force  exerted  by  freezing  water 
may  be  found  on  rocky  hillsides.  During  thaws  the  crevices  of  rocks  be- 
come filled  with  water.  As  the  weather  grows  cold,  this  water  freezes  and 
splits  the  rocks. 

Iron  water  pipes  are  sometimes  burst  by  the  freezing  of  the  water  in  them 
during  extremely  cold  weather. 

Capacity  of  Water  for  Absorbing  Heat.  —  Two  effects  may  be 
produced  by  the  application  of  heat  to  a  body:  (i)  a  rise  of 
temperature  which  is  generally  accompanied  by  expansion  of 
the  body  ;  thus  an  iron  rod  placed  in  the  fire  grows  warm,  and 
at  the  same  time  becomes  longer  and  thicker ;  (2)  a  change  of 
form ;  in  this  case  the  heat  given  to  the  body  changes  it  from 
a  solid  to  a  liquid,  or  from  a  liquid  to  a  vapor,  without  altering 
its  temperature. 

We  are  familiar  with  the  fact  that  a  kettle  of  boiling  water  may  be  kept 
boiling  for  a  long  time  before  all  of  the  water  is  changed  into  vapor,  yet  during 
that  time  its  temperature  has  not  changed,  although  it  has  absorbed  a  large 
amount  of  heat.  If  the  vapor  thus  formed  be  condensed  to  a  liquid,  it  may  be 
shown  experimentally  that  the  same  amount  of  heat  will  be  given  out  as  was 
originally  absorbed. 

Heat  which  causes  change  of  form  without  altering  the  temper- 
ature is  called  latent  heat ;   that  which  is  absorbed  by  a  solid 


138  PRC^PF.RTTRS   OF    WATKR 

when  melting  being  known  as  the  latent  heat  of  iiwltiito;,  and  that 
which  is  absorbed  by  a  Hquid  when  becoming  a  vapor,  as  the 
latent  heat  of  7'aponsatioii. 

Take  a  lamp  which  affords  enough  heat  to  raise  the  temperature  of  one  pound 
of  water  1°  a  minute  and  let  us  call  that  amount  of  heat  a  iiint  of  //eat.  Now 
set  in  a  vessel  over  the  lamp  a  pound  of  ice  at  32°.  It  will  immediately  begin 
to  melt,  but  the  heat  does  not  warm  the  ice  or  the  water ;  it  only  melts  the  ice. 
At  the  end  of  143  minutes  all  the  ice  will  be  melted,  but  the  temperature  of  the 
water  will  still  be  32°  and  no  more.  Now.  what  has  become  of  all  the  heat 
received  from  the  lamp  during  these  143  minutes?  It  has  gone  to  convert  the 
solid  into  a  liquid  and  is  therefore  called  latent.  The  latent  heat  of  melting 
ice  is  therefore  143  units.  Now  let  the  lamp  continue  burning  as  before. 
In  180  minutes  the  temperature  will  be  raised  from  32"^  to  212°  and  the 
water  will  then  begin  to  boil.  180  units  of  heat  have  therefore  been  re- 
quired to  raise  the  temperature  of  the  water  from  its  freezing  point  to  its  boil- 
ing point.  If  now  the  boiling  water  be  kept  over  the  lamp  it  will  not  become 
hotter  but  will  gradually  change  into  vapor  and  at  the  end  of  966  minutes  more 
it  will  have  boiled  away.  Thus  the  latent  heat  of  evaporation  of  water  is  966 
units.  In  other  words  it  takes  as  much  heat  to  melt  one  pound  of  ice  as  it 
would  to  heat  143  pounds  of  water  one  degree,  and  as  much  heat  to  change 
one  pound  of  boiling  water  into  vapor  as  it  would  to  heat  966  pounds  of  water 
one  degree. 

Water  is  pecuhar  in  that  its  latent  heats  of  melting  and  evap- 
oration are  larger  than  those  of  any  other  substance  and  this 
is  of  special  importance  in  its  relation  to  natural  phenomena. 

Evaporation  and  Condensation.  —  From  the  above  statement  it 
will  be  seen  that  evaporation  exerts  a  cooling  influence  because 
ice  or  water  on  becoming  vapor  renders  heat  latent. 

Condensation  of  water,  on  the  other  hand,  exerts  a  warming 
influence.  As  has  been  frequently  noticed,  the  intense  cold  is 
mitigated  just  before  a  snowstorm.  This  is  due  to  the  conden- 
sation of  vapor  into  snow. 

It  has  been  computed  that  from  every  cubic  foot  of  vapor 
condensed,  and  frozen  into  snow,  heat  enough  is  set  free  to 
raise  more  than  100,000  cubic  feet  of  air  from  the  temperature 
of  melting  ice  to  summer  heat. 

Nature  makes  great  use  of  these  counter  ]:)roperties,  the  evapo- 
ration and  condensation  of  water.     She  stores  away  the  heat  of 


CIRCULATION'   OF   WATKR  1 39 

the  torrid  zone  anion<^  the  particles  of  vapor,  thus  cooling  the 
atmosphere.  Transported  by  winds  to  other  regions,  they  are 
there  condensed  into  rain  and  their  heat  set  free  to  warm  the 
air  and  modif\'  the  climate. 

The  Solvent  Power  of  Water  is  another  property  of  great  im- 
portance. The  forms  of  plant  and  animal  life  are  largely  built 
up  of  materials  which  enter  them  in  solution.  Water  acts  as 
a  vehicle  for  conveying  these  materials  into  the  living  system. 
It  is  essential,  therefore,  to  the  maintenance  of  life. 

Moreover,  by  the  solution  of  mineral  substances  water  pro- 
motes rock  decay  and  the  general  disintegration  of  the  earth's 
crust.  All  waters  })crcolating  through  rocks  or  flowing  upon 
the  surface  are  more  or  less  charged  with  mineral  matter  held 
in  solution. 

Circulation  of  Water.  —  The  readiness  with  which  water 
changes  its  form  and  passes  from  the  liquid  state  to  that  of 
vapor,  and  from  the  vaporous  to  the  liquid  state  again,  is  the 
means  whereby  a  constant  circulation  is  carried  on  from  the 
sea  to  the  land,  and  from  the  land  to  the  sea  again. 

It  waters  the  thirsty  lands ;  it  fills  the  springs  and  replenishes 
the  rivers.  Thus  some  portions  of  the  rainfall  find  their  way 
back  to  their  home  in  the  sea  through  river  channels ;  other 
portions,  evaporated,  rise  in  the  atmosphere  and  again  being 
cooled  descend  as  rain  or  snow. 

And  thus  most  of  the  waters  of  the  globe  come  out  of  the 
sea  as  from  a  reservoir  and  to  it  they  are  later  returned. 


XIV.     WATERS   OF   THE    LAND 


Ground  Water  and  Springs.  —  Only  a  portion  of  the  rain  which 
falls  upon  the  land  finds  its  way  directly  into  the  creeks  and 
rivers  leading  to  the  sea.     The  larger  part  sinks  into  the  earth, 


Diagrammatic  Illustration  of  a  Common  or  Gravity  Spring 

a  represents  an  impervious  layer  above  which  are  the  porous  beds  b,  c,  and  d.  Rain  wafer 
percolating  the  soil  and  porous  beds  appears  as  a  spring  s,  where  the  bed  a  is  cut  by 
the  valley. 

where  it  is  known  as  ground  water,  though  sooner  or  later 
much  of  it  again  reaches  the  surface,  chiefly  in  the  form  of 
springs.  Many  rocks  are  porous,  and  most  rocks  are  traversed 
by  cracks  and  especially  by  joints,  consequently  surface  water 
percolates  downward  until  its  further  progress  is  impeded  by 
an  impervious  layer.  Flowing,  now,  over  the  top  of  that 
layer  in  the  direction  of  its  incUnation,  the  water  wi"!!  appear 
as  springs,  or  a  line  of  seepage,  wherever  the  topography  is 
such  as  to  furnish  an  outcrop,  as  on  the  side  of  a  hill  or  valley. 
Should  the  rocks  be  alternately  porous  and  impervious  and 
incline  or  dip  toward  a  fault  fissure  appearing  at  the  surface 
at  a  lower  level  than  their  outcrop,  then,  under  certain  condi- 
tions, as  when  the  opposite  wall  of  the  fissure  is  composed  of 
compact  or  non-porous  rock,  the  water  will  completely  fill  the 
fissure  and  will  be  forced  out  at  the  surface  under  more  or  less 
pressure. 

140 


J 


GROUND   WATER  AND   SPRINGS 


141 


DiagrjVMMATIC  Illustration  of  a  Fissure  Spring 

In  the  figure  above  the  porous  beds  p,p  and  the  impervious 
beds  c,c,c,  outcropping  on  the  right  and  dipping  to  the  left,  on  ac- 
count of  a  fissure  of  displacement  or  fault,  abut  on  an  impervious 
mass  m.  The  rain  falHng  upon  the  outcrop  creeps  downward 
through  the  pervious  beds/,/  until  the  fissure  is  reached,  where 
the  water  is  forced  to  the  surface  as  a  spring  s  by  the  pressure  of 
that  in  the  reservoirs  r,r,r  behind  it.  As  will  be  shown  later, 
the  principle  is  identical  with  that  of  the  artesian  well. 


^;'  --^  .^ 
^^r   4 

*?•"•■■■  ■  -if 

;f^'^m  ^^?fi^ 

■K"             '~'^ 

An  Appalachian  Mountain  Spring 

This  beautiful  spring,  surrounded  with  ferns  and  other  forms  of  vegetation,  is  one  of  many 
on  the  Black  Mountains  of  North  Carolina.     From  United  States  Geological  Survey. 

The  springs  above  described  represent  two  types :  (i)  common 
or  gravity  springs  ;  and  {2)fissiire  springs. 


142 


WAVERS    OF  THE    LAND 


Tlie  depth  to  wliich  percolating  water  descends  is  surjjrising.  From  a 
deep  well  sunk  in  a  certain  district  of  France,  pieces  of  leaves  were  thrown  up 
b}-  the  first  gush  of  water  from  a  depth  of  about  400  feet.  These  leaves  were 
comparatively  fresh.  They  were  ascertained  to  liave  come  from  a  distance  of 
about  150  miles  from  the  spring. 

From  the  percolation  of  water  through  the  earth  arises  one  of  the  greatest 
difficulties  in  mining  operations.  Before  the  invention  of  steam  pumps  many 
coal  pits  in  England  were  abandoned  because,  as  the  miners  said,  tliey  were 
dnnvncd.  From  the  Comstock  mine  3.500.000  gallons  of  hot  water  had  to  be 
pumped  every  24  hours. 

Artesian  Wells  are  so  called  from  the  province  of  Artois  in 
France,  where  they  were  first  used.     As  in  the  case  of  fissure 

^    -P  c      p  c 


Section  of  an  Artesian    Basin 

/, /,  porous  beds;  c,  c,  impervious  beds  above  and  below/,/,  inclosing  the  reservoir,  r  ; 

L,  water  level;    If,  artesian  well. 

springs,  their  source  of  supply  is  porous,  usually  sandy,  beds 
inclosed  by  impervious  layers.  The  porous  beds  act  as  reser- 
voirs, and  their  outcrop  may  be  many  miles  distant  from  the 
region  in  which  the  wells  are  sunk.  Formerly  it  was  thought 
that  artesian  conditions  prevailed  only  in  basins,  as  illustrated 
in  the  figure  above,  and  that  when  the  upper  confining  layer  was 
penetrated  by  boring,  the  water  should  rise,  fountain  like,  in  the 
air.  Theoretically  it  should  reach  the  height  of  the  water  level 
in  the  reservoirs,  but  practically,  on  account  of  adhesion,  friction, 
and  the  resistance  of  the  air,  this  is  not  attained. 

It  will  be  readily  understood  that  the  larger  the  number  of 
wells  sunk  in  a  given  basin,  the  more  the  pressure  is  reduced 
by  the  increased  outward  flow  which  lowers  the  height  of  the 
water  in  the  reservoir. 

It  must  be  kept  in  mind  that  by  "reservoir"  is  not  meant  a  cavity  filled 
with  water,  but  a  porous  rock,  as  a  bed  of  sand  or  gravel,  saturated  with 
water.  Through  such  a  reservoir  water  flows  which  has  fallen  on  its  outcrop 
as  rain. 


i 


AKIESIAN    WELLS 


«43 


AKfKsiAN  Conditions  akisinc  i  kom  iiii-:  I'assage  ok  Hokols  Waikk-iikarinc; 
Beds  into  Imperviois  Beds 

/>,  porous  beds;  c,c,  impervious  beds  above  and  below  tiie  porous  water-bearing  beds 
inclosing  the  reservoir ;  c' ,  the  region  where  the  pervious  beds  gradually  pass  into 
impervious  beds;  r,  reservoir;  L,  L,  water  level ;    H',  artesian  well. 

It  is  now  well  known  that  a  complete  basin  does  not  furnish 
the  only  artesian  condition.  Beds  inclining  or  dipping  in  one 
direction  may  grad- 
ually pass  from  a 
porous  into  a  com- 
pact and  more  im- 
pervious state,  and 
if  inclosed,  as  in  the 
preceding  case,  a 
reserv^oir  may  be 
formed  as  indicated 
in  the  figure  above, 
from  that  part  of  the 
confined  beds  which 
is  porous.  This  res- 
ervoir likewise,  when 
penetrated,  will  fur- 
nish flowing  wells 
until  by  over-boring 
the  pressure  is  re- 
duced. Moreover, 
the  same  results  may 
be  attained  by  the 
penetration    of     in- 

,•1  11  artesian  WEI.I.  Al    WOONSOCKET,   Sol  Til    DAKOTA 

clmed    porous    beds       ^,    ,     ,.    ,  ,       ,       .      ,       ^      ,,  .    ,^ 

'  The  height  of  the  column  is  97  feet.    From  L^nited  States 

properly         inclosed,  "  Geological  Survey. 

-M.-i.  HHVs.  ueol;.  —  9 


144 


WATERS   OF  THE   LAND 


which  thin  out  and  disappear  at  some  point  beyond  the  artesian 
area,  as  in  the  figure  below. 

c 


Artesian  Conditions  arisini;  from  the  thinning  out  of  Water-bearino 

Beds 
/,  porous  beds  thinning  out  at  jr ;  r,  reservoir;   /.,  Z,,  water  level ;    H^,  artesian  well. 

Although  originally  applied  to  flowing  wells,  the  term  arte- 
sian is  not  now  so  restricted,  but  may  be  applied  to  any  deep 
well,  whether  flowing  or  not,  which  has  its  source  at  a  consider- 
able depth  below  the  surface  and  depends  upon  the  rainfall  at 
a  more  or  less  distant  point. 

Artesian  wells  have  been  of  the  greatest  value  in  many  countries,  especially 
in  arid  and  semiarid  regions,  where  they  have  furnislied  water  not  only 
for  drinking  purposes,  but  for  irrigation  as  well.  In  Algiers  through  bor- 
ings put  down  by  the  French  an  abundance  of  water  has  been  olitained  on 
the  margin  of  the  Sahara. 

In  many  parts  of  the  United  States  artesian  wells  are  in  common  use,  es- 
pecially in  California  and  Texas.  In  some  instances  the  water  is  obtained 
from  beds  dipping  beneath  the  sea  as  on  the  Atlantic  and  Gulf  coasts. 

Rivers  receive  their  waters  (i)  directly  from  the  rainfall  as  it 
runs  off  the  surface  in  the  form  of  wet-weather  tributaries  ; 
(2)  from  springs;  (3)  from  the  melting  of  snow  fields  and  glaciers. 

Most  rivers  are  said  to  originate  in  springs,  each  of  which 
pours  forth  a  contribution  in  the  form  of  a  little  streamlet. 
Influenced  by  gravity,  streamlets  seek  a  lower  level,  and  uniting, 
form  creeks  and  rivers  the  volumes  of  which  are  often  greatly 
increased  by  sudden  rainfalls  and  the  melting  of  snow  over 
a  large  area.  In  a  similar  manner  a  number  of  tributaries' 
blending  together  make  one  great  water  course.  Such  a  water 
course,  with  its  tributary  streams,  is  called  a  river  system. 

Erosion  means  the  eating  or  wearing  away  of  the  materials 


Ek(  )SIOX 


•45 


which  form  the  earth's  exterior.     This  is  brought  about  chieriy 
in  two  ways:  (i)  by  the  solvent  power  of  the  water;  and  (2)  by  its 
mechanical  action  when  in  motion.     These  two  combined  remove 
the  more  soluble  and 
softer     rocks     with 
ease;    and  even  the 
hardest  cannot  with- 
stand their  action. 

If  the  soluble  par- 
ticles of  a  rock  are 
dissolved  by  water, 
the  rock  disinte- 
grates and  crumbles 
awav.  When,  there- 
fore, a  stream  runs 
i  n  c  e  s  s  a  n  1 1  )^  over 
such  a  constantly 
dissolving  and  disin- 
tegrating rock,  it  is 
clear  that  erosion 
will  make  rapid 
progress.  Moreover, 
the  rocky  fragments 
torn  from  the  stream 
bed  by  the  mechan- 
ical action  of  the  flow- 
ing water,  especially  where  there  is  a  marked  descent,  are  whirled 
against  one  another  and  the  bottom  and  sides  of  the  channel. 

Thus  as  the  river  flows  on,  the  fragments  of  rock  become 
smaller  and  smaller.  In  the  upper  course  of  the  river  they 
may  be  of  considerable  size,  but  in  the  lower  course  they  are 
reduced  to  sand  and  silt. 

The  erosive  action  of  rivers  is  most  impressively  illustrated  by  the  excava- 
tion of  rocky  gorges.  That  of  the  Niagara  and  the  canyons  of  our  Western 
rivers  are  |)erhaps  the  most  striking  examples  that  can  be  offered. 

Tlie  Falls  of  Niagara,  it  is  evident,  were  at  one  period  about  seven   miles 


Chakacikkistic  Bed  of  a  Mountain  Stream 
Hickory  Nui  Creek,  North  Carolina. 


146  WATERS  OF  THE    LAND 

lower  down  the  stream  than  at  present.  The  vast  volume  of  water  that 
passes  over  the  diff,  now  falling  from  the  height  of  160  feet,  both  directly  and 
indirectly  is  a  powerful  eroding  agent.  By  it  the  gorge  has  been  cut  back- 
ward from  the  Ontario  scarp  towards  lake  Erie. 

Transportation.  —  The  finer  particles  of  eroded  matter  are 
carried  along  by  the  river  in  suspension ;  that  is,  simply  mixed 
with  the  water.  The  coarser  portions  are  rolled  onward  by  the 
current.     This  twofold  action  constitutes  transportation. 

A  river  will  transport  eroded  matter  to  a  greater  or  less  dis- 
tance, and  in  greater  or  less  quantity,  in  proportion  to  the  ve- 
locity and  volume  of  its  current.  Water  moving  at  the  rate  of 
eight  inches  per  second  will  carry  along  ordinary  sand.  If  the 
velocity  be  increased  to  1 2  inches,  it  will  roll  along  fine  gravel, 
while  a  current  having  a  speed  of  three  feet  a  second  can  sweep 
along  pieces  of  stone  as  large  as  eggs.     In  floods  masses  of  rock 

^as  large  as  a  house  have  been  moved. 

f'^  As  to  the  quantity  of  matter  transported,  it  is  estimated  that  of 
ykible  sediment  the  Rhone  carries  into  the  Mediterranean  more 
than  36,000,000  tons  annually,  and  of  salts  invisibly  dissolved, 
more  than  8,000,000  tons.  The  amount  of  silt  carried  into  the 
Gulf  of  Mexico  by  the  Mississippi  in  one  year  would  make  a  col- 
umn one  mile  square  and  241  feet  high,  and  if  the  sand  and 
gravel  urged  along  the  bottom  be  added,  268  feet. 

The  removal  of  this  matter  from  the  surface  of  the  valley  reduces  its  average 
level  one  foot  in  4638  years. 

Deposition.  —  The  materials  borne  or  rolled  along  by  rivers 
are  deposited  at  various  points  in  the  channel.  The  finer  por- 
tions, called  silt,  familiar  to  us  as  muddy  sHme,are  carried  down 
as  far  as  the  mouth  of  the  river.  Farther  up  the  stream  sandy 
particles  come  to  rest;  still  higher,  gravel  is  deposited  ;  and 
finally,  in  the  upper  course  of  the  river  we  find  stones  of  greater 
or  less  size. 

It  is  obvious  that  deposition  will  depend  very  largely  upon  the 
slope  of  the  river  bed  and  the  rapidity  of  the  current.  Any- 
thing that  checks  the  latter  favors  deposition. 


I 


DKPOSITION 


'47 


Changes  in  river  courses  are  a  frequent  effect  of  deposition. 
They  occur  especiallx'  in  ri\ers  that  flow  through  alluvial  lands. 
Very  often  the  course 
of  such  streams  is 
marked  by  what  arc 
termed  uicandcrs,  or 
sharjD  curves  resem- 
bling the  letter  S. 
The  lower  Missis- 
sippi presents  a  strik- 
ing illustration  of 
this.  In  some  cases 
portions  of  the  land 
are  carried  from  one 
side  of  the  river  to 
the  other,  giving  rise 
to  important  ques- 
tions of  ownership. 

Sometimes,  too, 
when  a  river  is  unusu- 
ally high,  it  may  cut  for 
itself  a  straight  course 
instead  of  following 
its  old  curves.  The 
portion  of  the  former 
channel  that  is  thus 
abandoned,  closed  by 
silt  at  each  end,  be- 
comes a  lake,  cres- 
centic  in  shape,  com- 
monly called  a  "  cut 
off  "  or  an  oxbow. 

Among  the  important  deposits  of  rivers  are  those  that  occur 
at  or  near  their  mouths,  whether  they  flow  into  the  sea  or  a 
lake.  Here  the  current  is  checked  by  contact  with  the  larger 
body  of  water,  and,  as  a  consequence,  the  silt  which  is  readily 


Meanders,  M,  and  Oxbow  Lakes,  O,  ok 
Mississippi 


148 


WATERS   OF  THE    LAND 


held  in  suspension  by  the  moving  water,  now  settles  to  the  bot- 
tom.    In  this  way  bars  are  formed. 

The  Mississippi,  and  all  the  rivers  of  the  United  States  that 
flow  directly  into  the  Atlantic  Ocean,  have  bars. 


A  Ml  \Mii  IvIm;  SiKi.wt,  Cri-)()KED  Ckki-k,  Cai.ifoknia 
Crooked  Creek  is  a  tributary  of  Owens  River  in  eastern  California.  Pts  valley  has  been 
cut  in  volcanic  rocks.  In  the  waste-fiJled  portion  the  stream  has  taken  on  the  mean- 
dering condition  of  maturity.  The  manner  in  which  such  streams  broaden  their  valleys 
is  well  shown  by  the  meander  extending  to  the  left  from  the  center  of  the  picture. 
From  photograph  by  Willis  T.  Lee,  United  States  Geological  Survey. 

So  great  is  the  amount  of  .solid  matter  brought  down  by  the  Mis.sissippi 
that  a  bar  no  le.s.s  than  two  and  a  quarter  miles  in  breadth  was  formed  off  one 
of  its  outlets  called  the  South  Pass.  Fleets  of  vessels  more  than  50  an 
number  might  sometimes  be  seen,  detained  on  the  bar  for  weeks,  waiting  for 
a  chance  to  go  to  sea,  or  to  enter  the  Pass.  The  operation  of  towing  a  ship 
into  the  deep  waters  of  the  Gulf  occupied  days,  and  in  some  cases  weeks. 

In  1875  Captain  Eads,  by  the  authority  of  Congress,  constructed  yV///V.y,  or 
long  walls,  which  narrowed  and  confined  the  current,  and  thus  gave  it  greater 
velocity,  and,  of  course,  greater  power  to  scour  out  the  channel  and  carry  off 
the  sediment  into  deep  water.  The  mouth  of  the  Danube  has  been  deepened 
by  jetties  so  as  to  admit  vessels  of  20  feet  draught. 


DEPOSITION 


149 


Again,  when  a  river 
encounters  a  lake  or 
other  body  of  still 
water,  where  the  silt 
deposited  is  not 
washed  away  by 
strong  currents,  there 
is  gradually  built  up 
a  fan-shaped  deposit, 
through  which,  later, 
the  stream  may  flow 
in  several  channels  or 
distributaries.  Such 
a  deposit,  from  its 
resemblance  to  the 
Greek  letter  (A)  of 
that  name,  is  called  a 
delta. 

The  Mississippi, 
the  Nile,  the  Ganges, 
the  Orinoco,  the  Dan- 
ube, the  Volga,  and 
many  other  rivers 
which  flow  into  in- 
land seas  or  gulfs 
protected  from  the 
sweep  of  the  tides 
and  ocean  currents, 
are  famous  for  their 
deltas. 

But  where  there  is 
a  very  strong  littoral 
or  shore  current,  it 
sweeps  off  the  sedi- 
ment as  fast  as  it 
enters    the    sea,    and 


o<oVv^ 


Till'   Dki.ia  ami  Ui^i  Kiiir  1  akih>  iH'    1  iik  xNii.i- 
The  delta  of  the  Nile  has  the  typical  A-shape. 


Delia  of  1  hk  Mississippi 

The  lightly  shaded  portion  is  covered  with  shallow 

water. 


ISO 


WATERS   OF  THE   LAND 


there  is  no  delta  formed.  This  is  the  case  with  the  Amazon, 
the  Plata,  and  with  all  the  American  rivers  that  empty  into  the 
Pacific  Ocean. 

The  area  of  deltas  is  often  very  large.  That  of  the  Missis- 
sippi is  about  13,000  square  miles.  One  third  of  it  is  still  in 
process  of  formation,  being  as  yet  only  a  sea  marsh. 


Section  of  the  Mississippi 

Sediment  is  deposited  not  only  upon  the  beds  of  rivers,  but  also  upon  their 
ijanks.  This  has  the  etTect  of  raising  the  banks  above  the  general  level  of  the 
neighboring  country.  In  some  portions  of  their  course  both  the  Mississippi 
and  the  Po  are  above  the  adjacent  fields.  The  land,  therefore,  slopes  from 
the  river  on  either  side,  and  one  goes  up  to  it  instead  of  down  to  it. 

Rapids.  Cascades,  and  Waterfalls.  —  These  terms  are  employed 


A  Diagrammatic  Illustration  of  Rapids 

The  arrow  indicates  the  direction  of  stream  flow.     The  outcropping  rocks  are  seen  in 

section. 

to  denote  the  more  or  less  violent  descent  of  streams  in  their 
passage  from  a  higher  to  a  lower  level. 

Rapids  are  formed  wherever  the  stream  bed  is  in  the  form  of 
a  series  of  steps,  as  from  the  successive  outcropping  of  hard 
strata  or  where  a  stream  plunging  down  a  declivity  is  more  or 
less  imj)eded  by  barriers  of  hard  rock.     The  rapids  above  and 


KAPIDS,   CASCADES,    AND    \VA  lERI- ALLS 


'51 


A   DiACkAMMAllC    ILIASI  KAl  ION    OK    CASLAUbS 

The  hard  layers  foi  ni  miniature  table  rocks  over  which  tiie  water  falls.  The  softer,  thin 
bedded  rocks  below  are  easily  eroded  so  that  each  cascade  represents  a  temporary 
stage  in  gorge  formation. 

below  Niao^ara    Falls  and  the  rapids   of    the    Saint    Lawrence 
River  afford  excellent  examples  of  this  form  of  stream  descent. 

A  cascade  is  a  low 
perpendicular  or  nearly 
perpendicular  waterfall, 
usually  one  of  a  series 
by  which  a  stream  rather 
abruptly  reaches  its  lower 
level.  Frequently  cas- 
cades result  from  the  al- 
ternation of  hard  and  soft 
strata  in  the  stream  bed. 
Falls  of  the  cascade  type 
are  especially  character- 
istic of  the  lake  region  of 
central  New  York.  The 
glens  and  gorges  about 
the  heads  of  Cayuga  and 
Seneca  lakes  afford  many 
beautiful  examples. 

The  typical  waterfall  is 
perpendicular,  resulting 
from  the  abrupt  descent 
of  a  stream  over  a  preci- 
pice. In  regions  of  strat- 
ified rocks  the  plunge 
may   be    over    hard    rock  Cas.a,>k  in  niv.  Catskm.i.s 


152 


WATERS   OF   THE   LAND 


( 


Thk  American  and  Luna  Falls,  Niagara,  from  below 
In   tin;   foreground   is  the  "  Rock   of  ARes,"   one  of  the  largest  of  the  fallen  limestone 

fnigments. 


RAl'IDS.    (   AS(  Alii;>.    AMI    WMKKIAI. 


'53 


\\  iiiki.i  uui,  Kaiiijs,  Niagara  Ri\kk 
From  a  photograpli. 


layers  (table  rock)  which  are  underlain  by  softer  beds.  Such  is 
the  case  at  Niagara.  Here  the  harder  upper  rock  is  a  limestone  80 
feet  thick.     Beneath  it  there  is  a  softer  rock,  of  about  the  same 


54 


WATERS   OF  THE    LAND 


Gkkat  Falls  of  iul  Vkllowsio.nl 
From  pliotograpli  by  Haynes. 


I.AKKS 


155 


thickness,  made  up  of  very  thin  layers,  known  as  shale.     As  the 

limestone  is  undermined  by  the  breaking  up  of  the  shale  by  frost 

and  water  action  great  fragments  of  the  table  rock  drop  into  the 

abyss  below,  and   thus  the   falls   gradually  retreat   up   stream. 

Other  forms  of  per- 

})cndicular    falls,     as 

in  the  \'osemite,  are 

caused     by     streams 

leaping   into   a  great 

valley    excavated    b\' 

glacial   action. 

In  regions  of  igne- 
ous rocks  waterfalls 
often  result  from  the 
unequal  resi.-i'tance  of 
the  layers  forming 
the  stream  bed.  A 
very  hard  layer,  such 
as  basalt,  overlying 
soft  and  non-resisting 
layers,  will  give  rise 
to  the  typical  per- 
pendicular fall  as  in 
the  case  of  the  Sho- 
shone Falls  of  the 
Snake  River.  In 
rather  unusual  instances  dikes  or  walls  of  hard  igneous  rocks 
form  the  barrier  over  which  streams  are  precipitated,  as  exempli- 
fied in  the  Lower  or  Great  Falls  of  the  Yellowstone. 

The  Victoria  Falls  of  the  Zambezi  in  Africa  are  the  most 
remarkable  in  the  world.  They  are  more  than  a  mile  wide  and  over 
400  feet  in  perpendicular  height.  The  river  plunges  into  a  nar- 
row ravine  running  diagonally  across  the  river  bed. 

Lakes.  —  The  formation  of  lake  basins  has  been  ascribed  to 
many  causes,  some  of  which  are  as  follows :  ( i)  great  (diastropJiic) 
movements  of  the  earth's  crust,  especially  those  producing  large; 


IrnAiA  Fai.i,.  Xkw  York 
This  is  a  fall  of  the  cascade  type. 


156 


WAI'ERS   OF  THE    EAND 


downward  folds;  (2)  the  obstruction  of  drainage  by  the  elevation  of 
mountains  ;  (3)  subsidence,  as  in  certain  regions  affected  by  earth- 
quakes ;  (4)  the  damming  of  valleys  by  glacial  barriers  (moraines) 


Niagara  Falls  in  Wintlr 
The  severity  of  the  winter  is  shown  by  the  great  accumulation  of  ice  Ijelow  the  falls. 

left  upon  the  retreat  of  the  ice;  (5)  depressions  in  glacial  drift 
due  to  the  melting  of  isolated  patches  of  ice  ;  (6)  glacial  erosion  ; 
( 7)  volcanic  action. 

Lake  Superior  is  thought  to  occupy  a  great  downward  fold  of  the  earth's 
crust,  or  syncline.  Most  of  the  lakes  in  mountainous  regions  have  resuhed  from 
orographic  movements.  The  lakes  of  the  -sunk  country"  near  New  Madrid. 
Mo.,  sprang  into  existence  as  a  result  of  the  well-knownearthquake  of  i8[i-i2. 
In  Switzerland  and  other  mountainous  regions  small  lakes  behind  ghtcial  bar- 
riers are  known.  The  numerous  lakelets  and  ponds  in  glacial  drift,  as  in  Mas- 
sachusetts, are  due  to  the  melting  of  isolated  patches  of  ice  which  were  left 
surrounded  or  buried  in  debris  upon  the  retreat  of  the  glacier.  Some  of  the 
lakes  of  central  and  western  New  York,  as  Cayuga  Lake,  .seem  to  be  due.  in  part 
at  least,  to  the  formation  of  rock  basins  by  glacial  erosion.  Crater  Like,  in  the 
Cascade  Range  of  southern  Oregon,  and  similar  Jakes  in  other  parts  of  the 
world,  (jccupy  extinct  volcanic  vents. 


KkESII-WArKk    A\l»    SALl-WAlKk    lAKKS 


157 


Fresh-water  and  Salt-water  Lakes.  —  In    regions  where  the 
precipitation    or    rainfall   exceeds  the  evaporation,    lake   basins 


'f^ 

^^ 

MH 

witk 

M 

MH 

^^R.^^ 

^ 

91 

^M 

8^-- 

I^^SH 

hI 

|^^^^B|Un|M^«-'%^|M 

^^^^^^^^HK^  .ii.^K'; 

^  <^^^^^^^^^^H 

f^^W^^i 

H^^ 

ill 

^^^H.<:iK.- 

P^la 

^^ift^E 

fl 

^^^^^^^^  ^^B 

^^^         <)d^^^^l 

1    J 

YosEMiTE  Falls,  C.\i,ifornl\ 
The  height  of  tlie  upper  falls  is  about  1500  feet. 

will  be  filled  with  water  which,  overflowing  the  rim  or  breaking 
through  the  barrier  at  some  weak  point,  pushes  onward  to  the 


158 


WATERS   Ob     THl:;    LAM) 


sea,  cutting,  it  may  be,  a  channel  through  hard  rocks;   hence  the 
presence,  oftentimes,  of  rapids,  waterfalls,  and  gorges. 

In  the  case  of  lake  basins  situated  in  arid  regions,  which  are 
characterized  by  great  warmth  and  dryness,  the  amount  of  water 


Cnstle  of  Chillon,  Cake  Geneva.     Dent  du  Midi  in  the  background. 

evaporated  is  sometimes  equal  to  that  which  is  supplied,  and 
sometimes  greater.  As  fast  as  the  water  is  poured  into  these 
basins  by  the  rivers  it  is  carried  away  in  the  form  of  vapor. 
Such  basins  are  not  filled  to  overflowing,  and  consequently 
have  no  outlets. 

The  water  of  lakes  having  no  outlets  is  commonly  salt.  The 
water  of  lakes  having  outlets  to  the  sea  is  fresh.  The  reason  for 
this  will  be  readily  understood  from  the  following  explanation. 
Rivers  carry  into  lakes  many  substances  in  solution,  of  which  one 
of  the  most  common  is  chloride  of  sodium,  or  common  salt.    This 


IKtSll-WArEK    AND    >AL1'   WAIK 


LAKES 


159 


is  Drcsent  in  ordinal-)'  river  water,  although  it  cannot  be  tasted  ; 
l)iit  if  a  large  quantity  of  such  water  were  evaporated,  a  small 
amount  of  salt  would  be  left  behind.  Thus  it  is  clear  that  if 
a  lake  have  an  outlet,  not  only  is  its  superfluous  water  removed, 
but  the  salts  dissolved  in  such  water  are  also  taken  out. 


I'HE  Dead  Se.v 


On  the  other  hand,  if  a  lake  have  no  outlet,  then,  while  the 
water  brought  in  is  removed  by  evaporation,  the  salt  intro- 
duced remains  behind.  Thus  lakes  having  no  outlet  may  be 
compared  to  the  evaporating  vats  or  troughs  in  which,  as  at  many 
points  on  the  shores  of  the  Mediterranean,  sea  water  is  boiled,  or 
evaporated  by  solar  heat,  in  the  manufacture  of  salt.  The  water 
passes  off,  the  salt  remains.  Hence,  year  after  year,  salt  lakes 
become  Salter. 

Conspicuous  examples  of  salt  lakes  are  the  Great  Salt  Lake  and  the  Dead 
Sea.     Both  of  these  are  heavily  charged  with  saline  ingredients.     The  water 

M.-S.  PHYS.  GEOG.  —  lO 


i6o 


WATERS    OF  THE    LAND 


of  the  Dead  Sea  is  about  one  fifth  heavier  than  that  of  the  ocean,  and  sustains 
tlie  human  body,  so  that  it  cannot  sink  in  it.  From  its  great  salinity  the  Dead 
Sea  is  often  called  the  Sea  of  Salt.  But  the  Jordan,  which  supplies  it,  is  of 
course  fresh. 

The  Dead  Sea  is  situated  in  a  depression  remarkable  for  its  intense  heat,  and 
the  reo-ion  in  which  the  Great  Salt  Lake  lies  is  very  remarkable  for  the  dryness 
of  its  atmosphere.  In  the  case  of  both  these  lakes,  therefore,  evaporation 
proceeds  at  an  enormous  rate. 


Cayuga  Lake  from  Cornei.i,  Heights,  Ithaca,  N.Y. 


Inland  Seas.  —  Some  inland  bodies  of  sn1t  water,  however, 
have  evidently  been  at  one  time  parts  of  the  ocean.  These  are 
properly  designated  inland  seas.  The  most  remarkable  of  them 
are  the  Caspian  and  Aral. 

When  the  Arctic  Ocean  extended,  as  geologists  believe  it  did, 
southward  as  far  as  the  mountains  of  Persia,  these  two  seas  and 
many  neighboring  bodies  of  salt  water  were  included  within  its 
limits. 

Seals  abound  in  the  Caspian,  and  sturgeons,  herrings,  and 
other  sea  fish  in  both  the  lakes. 

Like  other  salt  lakes,  these  inland  seas  have  no  outlet.     The 


DESKCATKD   t)K    EVAPORATED    LAKES  l6l 

Volga,  the  largest  river  in  Europe,  and  the  Ural  pour  volumes  of 
water  into  the  Caspian,  yet  its  level  does  not  rise.  Lake  Aral 
receives  the  Amu  and  Syr  rivers,  yet  its  level  seems  actually 
to  be  lower  than  formerly. 

Many  small  salt  lakes  entirely  evaporate  during  the  summer, 
and  leave  their  beds  covered  with  saline  incrustations.    From  the 


Crater  Lake,  Oregon 
This  unique  body  of  fresh  watt-r  is  situated  in  the  Cascade  Range  of  southwestern  Oregon. 
Occupying  a  depression,  known  as  a  caldera,  formed  by  the  subsidence  or  caving  in 
of  a  great  volcanic  summit — Mount  Mazama  —  its  surface  is  6,239  '^^^  above  sea 
level.  Its  shape  is  somewhat  elliptical,  its  diameters  being  6\  and  4J  miles  respectively. 
Its  depth  approximates  2,000  feet.  A  single  island,  in  the  form  of  a  cfnder  cone,  rises 
aijove  its  waters.  There  is  no  outlet,  the  steep  walls  of  the  caldera  rimming  the  lake 
on  all  sides. 

dry  bed  of  Lake  Elton,  in   the  Caspian  region,  100,000  tons  of 
salt  are  annually  gathered. 

Desiccated  or  Evaporated  Lakes.  —  Salt  and  alkaline  lakes 
are  usually  the  remnants  of  larger  bodies  of  water  which  have 
greatly  shrunken  or  almost  disappeared  on  account  of  the  arid- 
ity brought  about  by  climatic  changes.  The  former  existence 
of  such  lakes  is  shown  b)'  easily  recognized  basins  and  shore 
lines,  as  in  the  case  of  Lake  Bonneville,  in  Utah,  and  Lake  La- 


l62 


WATKRS   OK    THE    LAND 


hontan,  in  Nevada.  Great  Salt  Lake  is  a  survival  of  the  former, 
while  Carson,  Pyramid,  Winnemucca,  Humboldt,  and  other  lakes 
fill  depressions  in  the  basin  of  the  latter. 


A  Caldera,  Canary  Islands 

Calderas  or  "  caldrons  "  are  large  craterlike  depressions  which  often  measure  several  miles 
in  diameter.  In  sime  instances  they  seem  to  have  resulted  from  violent  eruptions, 
during  which  volcanic  summits  have  been  blown  completely  away;  in  others,  they 
have  evidently  been  formed  by  the  subsidence  or  caving  in  of  volcanic  cones.  See 
Crater  T.ake. 


The  waters  of  Lake  Bonneville,  which  were  fresh,  flowed  into  Snake  River. 
Lake  Lahontan  had  no  outlet  and  its  waters  were  probably  never  fresh.  As 
these  lakes  diminished  in  volume,  the  water  became  more  and  more  concen- 
trated, until  tlie  mineral  matter  held  in  solution  was  precipitated.  The  first 
substance  deposited  was,  carbonate  of  lime  in  the  form  of  tufa.  This  is  found 
along  the  ancient  shores  of  Lake  Bonneville  and  in  much  greater  abundance 
along  those  of  Lake  Lahontan.  Great  Salt  Lake  is  rich  in  salt  (sodium 
chloride)  ;  the  Nevada  lakes  are  not.  As  an  explanation  of  this  difference,  it 
as  been  suggested  tliat  Lake  Lahontan  had  probably  been  evaporated  to  dry- 


OFIICKS    OF    l.AKKS 


■^>3 


ness.  truly  i/t'sura/t'(/,dnd\.hdi  later,  underslightl\  t'liaii;^(.:(l  climatic  cunditions, 
whicli  permitted  the  formation  of  smaller  bodies  of  water,  the  salt  beds  that 
must  have  existed  were  buried  under  clav  de])osits.  and  therefore  do  not  affect 
the  waters  of  the  present  lakes. 

Offices  of  Lakes.  —  Lakes    act    as    lesei'voirs  and    thus  often- 
times prevent  the  flooding  of  rivers.      The  waters  of  the  upper 


Ui'PKK   Lake  uf  Kii.i.ak.nkv,  Ikkianh 

The  Iraki's  of  Killninev  are  famous  for  their  beauty.     They  He  in  tlie  souihui'Stern  part  of 

Ireland  about  35  miles  nortlnvest  from  Cork. 

tributaries  of  a  stream,  swollen  by  recent  and  heav\'  rains  or  b)' 
the  rapid  melting  of  snow,  upon  reaching  a  lake  spread  out  and 
are  held  back,  in  consequence  of  which  the  flow  at  the  outlet  is 
not  greatly  increased.  As  the  inundations  of  the  lower  Missis- 
sippi are  mainly  due  to  the  floods  of  its  tributaries,  there  being 
no  intervening  lakes  to  hold  back  the  surplus  waters,  it  has  been 
proposed  to  regulate  its  flows  by  the  erection  of  impounding 
reservoirs  on  its  headwaters. 

Furthermore,  lakes  act  as  settling  basins.     The  water  flowing 


164  WAIKRS    ()!•     rilK    LAND 

into  a  lake  may  be  laden  with  sediment,  even  the  finest  glacial 
silt,  but  the  water  flowing  from  it  will  be  clear,  containing  no 
matter  held  mechanically  in  suspension.  Hence  it  follows  that 
a  lake  may  become  completely  filled  with  detritus  brought  in  by 
flowing  streams.  When  this  stage  has  been  reached,  the  lake 
gives  place  to  a  plain  through  which  the  supplying  stream 
meanders.  This  is  illustrated  in  a  small  way  by  the  accumula- 
tions deposited  in  the  reservoir  behind  an  old  dam. 

Geographical  Distribution  of  Lakes.  —  In  North  America  are 
found  the  vast  bodies  of  fresh  water  which  are  called  the  "Great 
Lakes." 

Lake  Superior,  a  member  of  this  group,  is  the  largest  body  of  fresh  water 
in  the  world.  Its  area  is  over  30,000  square  miles.  The  surface  of  this  great 
inland  sea  has  an  altitude  of  602  feet,  but  its  bottom  extends  below  the  sea 
level  406  feet. 

The  northern  part  of  the  Great  Central  Plain  of  the  continent 
abounds  in  lakes  of  greater  or  less  magnitude.  In  the  basin 
l>etween  the  Rocky  Mountains  and  the  Sierra  Nevada  there  is  a 
region  of  saline  lakes. 

In  Europe,  the  great  lake  region  lies  in  northern  Russia  and 
Scandinavia.  Ladoga  and  Onega,  Wener  and  Wetter,  are  the 
largest  lakes  of  the  grand  division.  Those  of  the  Alps,  Como, 
Miiggiore,  Geneva,  and  others  are  comparatively  small,  but  famed 
for  their  beauty. 

Asia  is  noted  for  the  size  and  number  of  its  salt  lakes.  The 
Caspian  Sea,  Lake  Aral,  and  the  Dead  Sea  are  examples. 

Of  fresh-water  lakes  Asia  has  few.  Lake  Baikal,  however, 
400  miles  in  length,  may  be  compared  with  our  own  Lake 
Superior. 

Africa  rivals  North  America  in  the  magnitude  of  her  great 
lakes.  Victoria  and  Albert  Nyanza,  Tanganyika  and  Nyassa, 
are  the  largest. 

South  America  has  one  lake  of  importance,  Titicaca.  Aus- 
tralia is  noted  for  its  salt  lakes.  Eyre,  Torrens  and  Gairdner 
each  exceed  100  miles  in  length. 


XV.     DRAINAG?: 

Advantages  of  Drainage.  —  The  drainage  of  the  land  depends 
primarily  upon  its  relief.  Those  countries  best  adapted  for 
human  habitation  are  well  drained.  Crops  do  not  flourish  on 
cold,  damp  soils,  nor  can  human  health  and  strength  be  main- 
tained where  the  ground  is  always  wet.  As  is  well  known,  the 
vicinity  of  swamps  is  especially  unhealthful. 

For  this  reason  a  very  large  area  of  the  sunny  peninsula  of 
Italy,  called  the  Campagna,  once  densely  populated,  is  almost 
uninhabited.  From  the  days  of  ancient  Rome  it  has  remained, 
owing  to  the  level  nature  of  the  land,  and  the  consequent 
absence  of  any  stream  into  which  the  waters  might  be  directed, 
a  vast  swamp  and  a  breeding  ground  of  pestilence.  It  is  now 
being  reclaimed. 

How  Drainage  is  Effected.  —  Rivers  are  the  channels  through 
which  the  water  carried  from  the  sea  in  the  form  of  vapor  and 
rained  upon  the  land  finds  its  way  back  to  the  sea.  Every 
running  stream  may  therefore  be  regarded  as  a  kind  of  rain 
gauge,  which  measures,  in  a  general  way,  the  quantity  of  rain 
that  falls  upon  the  valley  which  it  drains. 

The  region  drained  by  a  river  system  is  called  the  river  basin. 
The  basins  of  large  streams  are  hundreds  of  thousands  of  square 
miles  in  area.  That  of  the  Mississippi  contains  nearly  1,250,000 
square  miles. 

The  limits  of  a  river  basin  are  defined  by  what  are  termed 
zuatersheds ;  that  is,  water  divides,  j//r^/ being  from  a  German  word 
meaning  to  divide.  A  watershed  is  a  line  of  elevation,  some- 
times lofty  and  sometimes  low,  which,  like  the  ridge  of  a  roof, 
divides  the  rain  as  it  falls,  and  causes  one  portion  to  descend  one 
slope  of  a  country  or  continent,  and  the  other  portion  another. 

165 


1 66 


r)RAiNA(;t: 


If  on  a  map  of  North  America  you  trace  a  pencil  line  round  the  sources  of  all 
the  rivers  that  pour  into  the  Mississippi  from  the  Appalachian  slope  on  the  one 
side,  and  from  the  Rocky  Mountain  slope  on  the  other,  30U  will  have  marked 
out  the  watersheds  which  define  the  eastern  and  western  limits  of  the  Mis- 
sissippi basin. 

The  mountains  and  slopes  of  every  country  determine  in  a 
Inrge  measure  the  number  of  its  water  courses,  their  length  and 
direction,  and  the  velocity  of  their  currents  ;  in  a  word,  their 
capacity  for  carrying  off  superfluous  rain  water. 

Inundations. — The  inundations  or  floods  which  occasionally 

submerge  large  areas 
of  land,  and  are  so 
destructive  to  life  and 
property,  occur  where 
the  quantity  of  water 
to  be  removed  exceeds 
the  capacity  of  the 
draining  rivers.  Many 
rivers,  as  the  Nile, 
the  Orinoco,  and  the 
Mississippi,  are  sub- 
ject to  periodical  over- 
flow. So  extensive 
are  the  inundations 
of  the  Po  that  the 
Italian  engineers  have 
actually  proposed  a 
scheme  for  cutting  an  artificial  channel  to  be  used  in  case  of 
cmergenc}'. 

The  chief  causes  of  floods  are  to  be  -found  in  seasonal 
changes.  They  affect  the  rainfall  and  cause  the  melting  of 
snow  both  on  high  mountains  and  in  river  basins.  The  sudden 
disappearance  of  winter  snow  is  always  accompanied  by  swollen 
streams. 

The  meltinL;  (ifsiKAv  in  Ft- nnsylvania.  Oiiid,  Indiana,  antl  Illinois,  togellicr 
with  copious  sprint^  rains,  are  annuall\'  followed  hv  a  marked  rise  in  ihe  Ohio 


Fl.OODKD    LaNUS    at    SINCAC,    Nl'.W    JKKSEY,    ON   THK 

Passaic  Rivkk 
Fiom  United  States  Geological  Survey. 


NOR  111    A.Ml-.RICA  167 

and  its  tributarifs.  and  wlicn  the  snows  of  the  Rocky  Mountains  begin  to 
nielt,  the  western  tributaries  ot  the  Mississippi  are  Hooded  and  that  stream 
experiences  the  "June  rise." 

North  America.  —  The  boundin^^  waters  of  North  America 
are  the  Arctic  Ocean,  the  Pacific  Ocean,  and  the  Atlantic, 
including  the  (nilf  of  Mexico.  These  receive  the  drainage  of 
the  grand  division. 

The  great  watershed  is  the  Rocky  Mountain  system.  It  acts 
like  the  ridge  of  a  roof,  shedding  the  water  to  the  east  and 
to  the  west.  All  the  region  lying  westward  of  it  is  drained 
into  the  Pacific  and  into  Bering  Sea  by  the  Colorado,  the 
Columbia,  the  Phaser,  the  Yukon,  and  other  rivers  of  less  im- 
portance. 

East  of  the  Rocky  Mountains  the  grand  division  is  divided 
into  four  .slopes:  a  northern,  inclining  toward  the  Arctic  Ocean  ; 
a  northeastern,  toward  Hudson  Bay  ;  an  eastern,  toward  the 
Atlantic  ;    and  a  southern,  toward  the  Gulf  of  Mexico. 

The  largest  river  draining  to  the  Arctic  is  the  Mackenzie. 
The  Saskatchewan-Nelson  is  the  chief  system  draining  to 
Hudson  Bay.  To  the  south  lies  the  great  basin  of  the  Missis- 
sip])i,  the  drainage  of  which  is  poured  into  the  Gulf.  This  basin 
embraces  the  enormous  area  which  lies  between  the  Rockv 
Mountains  and  the  Appalachians. 

The  amount  of  water  carried  by  the  Mississippi  from  this  region  into  the 
Gulf  of  Mexico  every  second  is  675.000  cubic  feet,  enough  to  cover  about  iS 
acres  of  ground  to  the  depth  ot  a  foot.  We  can  see  from  this  how  soon  tlie 
.Mississippi  basin  would  become  a  desolate  swamp.  If  it  were  a  dead  levt-l 
untrenclied  by  its  mighty  system  of  rivers. 

The  eastern  slope  of  the  grand  division,  including  the  terraced 
plateau  occupied  b}'  the  Great  Lakes,  is  drained  by  the  Saint 
Lawrence  and  by  a  series  of  rivers,  large  and  small,  which  flow 
from  the  Api)alachians  to  the  Atlantic. 

South  America.  — The  drainage  of  South  America,  like  that  of 
North  America,  is  maiiil\-  effected  by  three  river  systems.     The 


l68  DRAINAGE 

crest  of  the  Andes  is  the  great  watershed.  It  lies  along  the 
western  edge  of  the  grand  division.  Hence  the  drainage  has 
in  general  an  easterly  flow. 

The  eastern  slope  embraces  nearly  the  whole  of  the  grand 
division.  It  is  divided  into  three  great  river  basins,  those  of 
the  Orinoco,  the  Plata,  and  the  Amazon.  The  last  contains  the 
greatest  river  system  on  the  globe. 

The  Amazon  discharges  six  times  as  much  water  as  the  Mississippi.  In 
respect  to  volume  it  is  the  largest  river  in  the  world.  It  rises  in  the  beautiful 
little  lake  of  Lauricocha,  high  up  among  the  Andes.  Descending  by  falls 
and  rapids,  it  reaches  the  region  of  the  silvas,  and  then  becomes  a  stream 
navigable  for  large  steamers  from  the  foot  of  the  mountains  to  the  sea,  a 
distance  of  about  2200  miles. 

So  great  is  the  force  of  its  current  that  its  fresh  waters  are  carried  a  dis- 
tance of  about  200  miles  from  the  land.  An  ocean  current  passing  near  its 
mouth  sweeps  away  sediment  as  fast  as  the  river  brings  it  down.  Thus 
the  river's  own  current  and  the  ocean  current  prevent  the  formation  of  a  bar. 

The  western  slope  of  South  America  is  steep  and  narrow. 
There  is  no  room  for.  long  rivers,  and  no  water  for  large  rivers. 
The  Pacific  receives  only  a  few  small  mountain  torrents,  fed  by 
the  melting  snows  of  the  Andes. 

Europe.  —  From  a  point  in  the  Ural  Mountains  at  about 
latitude  61°  north,  to  the  Valdai  Hills,  thence  in  a  southwest- 
ward  direction  through  central  Europe  down  to  the  southern 
shores  of  Spain,  an  irregular  line  may  be  traced  which  will 
separate  Europe  into  two  great  slopes.  The  one  inclines  to  the 
northwest,  the  other  to  the  southeast. 

All  the  rivers  have  one  or  the  other  of  these  two  general 
directions  ;  and  the  grand  division  is  drained  into  the  Mediter- 
ranean, the  Adriatic,  the  Black,  and  Caspian  seas  on  the  one 
side  ;  or  into  the  Atlantic  and  Arctic  oceans,  and  the  North, 
Baltic,  and  White  seas  on  the  other. 

The  region  of  the  Alps  is  drained  by  four  streams,  the  beauti- 
ful Rhine  of  the  Germans,  the  Rhone,  the  Danube,  and  the  Po  ; 
the  drainage  of  the  low  jjlains  is  accomplished  by  a  number  of 
rivers,  among  which  the  Volga,  the  Don,  the  Dnieper,  and  the 
Dniester  are  conspicuous. 


ASIA 


169 


Asia.  —  The  grand  division  of  Asia,  like  that  of  Europe,  may  be 
regarded  as  consisting  of  two  great  slopes,  one  having  a  general 
incline  toward  the  north,  the  other  toward  the  south  and  east. 

Beginning  on  the  western  shore  of  Asia  Minor,  a  line  may  be 
drawn  to  Mount  Ararat,  thence  along  the  crests  of  the  Klburz 
and  Hindu  Kush  Mountains,  thence  northeastwardly  to  the  Sea 


View  on  the  River  Nile 
Water  carriers  filling  their  "  skins." 

of  Okhotsk,  which  will  represent  the  great  watershed  of  the 
grand  division. 

Southeast  of  this  line  the  Euphrates  and  Tigris,  the  Indus, 
Ganges,  the  Yangtse,  the  Hoang,  and  Amur  carry  the  drainage 
to  the  southward  and  eastward  into  the  seas  and  bays  of  the 
Pacific  and  Indian  oceans. 

On  the  northern  side  of  the  line  nearly  every  important  river 
flows  in  a  northerly  direction  into  the  Arctic  Ocean. 

Africa.  —  The  drainage  of  Africa  is  accomplished  in  the 
main  by  the  four  great  river  systems  of  the  Nile,  the  Niger,  the 


170 


DRAINAGE 


Kongo,   and  the  Zambezi.      Much  of  the  surpkis  water  of  the 
grand  division,  however,  is  removed  by  evaporation. 

The  most  interesting  feature  in  the  drainage  system  of  Africa  is  the  river 
Nile.  But  for  it  Egypt  would  be  as  barren  as  the  Great  Desert  of  Sahara. 
The  river  is  formed  by  the  junction  of  two  streams  called  the  White  and  the 
Blue  Nile.  The  former  issues  from  the  Equatorial  Lakes.  The  latter  rises 
among  the  hills  and  the  table-lands  of  Abyssinia. 

During  June.  July,  and  August  the  rains  pour  down  in  torrents  upon  the 
regions  drained  by  these  streams.  Each  is  flooded.  Uniting  at  Khartum,  the 
descending  torrents  reach  Cairo  by  the  middle  of  June,  and  during  the  latter 
part  of  summer  and  in  the  autumn  the  land  of  Egypt  is  uijder  water. 

As  the  flood  subsides,  a  layer  of  fertilizing  sediment  is  deposited  upon  the 
soil.  Most  of  it  has  been  washed  down  from  the  Aby.ssinian  hills  by  the  Blue 
Nile,  which  takes  its  name  from  the  color  which  the  sediment  imparts  to  its 
waters. 

Australia  is  scantily  supplied  with  rivers.  The  Mui-ray  and 
its  tributaries  are  the  only  water  courses  of  importance.  Dur- 
ing times  of  drought  the  latter  cease  to  flow  and  the  main  stream 
is  greatly  shrunken. 


XVI.     THK    SKA    AND    THK    OCEANS 

Extent  of  the  Sea.  —  Less  than  three  fourths  of  the  earth's 
surface  is  covered  by  water.  This  surface  comprises,  in  round 
numbers,  an  area  of.  197,000,000  square  miles,  of  which  about 
55,000,000  are  land  and  142,000,000  water.  All  of  the  land,  ex- 
cept 13,000,000  square  miles,  is  on  the  north  side  of  the  equator. 
The  northern  hemisphere  therefore  contains  approximately  three 
fourths  of  all  the  known  land,  and  two  fifths  only  of  the  water 
surface,  of  the  world. 

The  extent  of  water  that  is  visible  to  the  eye  at  one  time  is  not  great.  If 
we  stand  on  the  shore  and  look  seaward,  oar  view  is  closed  in  bv  a  line  in 
which  sea  and  sky  appear  to  meet.  To  this  line  we  give  the  name  horizon; 
that  is.  bounding  line.  Its  distance  from  us  depends  on  our  elevation.  If  wl- 
occupy  a  position  which  is  elevated  six  feet  above  the  sea  level,  our  horizon 
will  be  three  miles  oflF.  If  we  ascend  a  bluff  or  lighthouse,  and  so  gain  a  point 
about  100  feet  high,  our  horizon  will  be  12  miles  distant. 

Saltness  of  the  Sea. — Various  solids  ai-e  found  dissolved  in 
sea  water.  Of  these  the  most  abundant  is  common  salt.  Others 
are  certain  compounds  of  lime,  magnesium,  potassiinn,  and 
iodine.  The  solid  matter  may  be  estimated  on  an  average  as 
about  one  thirtieth  ])art  of  the  whole  bv  weight. 

Though  there  is  little  variation  from  the  average,  it  seems 
to  be  well  ascertained  that  there  are  areas,  as  within  the  region 
of  the  North  Atlantic  trade  winds,  for  example,  where  the  pro- 
portion of  saline  matter  is  greater  than  elsewhere.  This  may 
be  expected,  since  evaporation  ^  is  there  at  its  maximum.  On 
the  other  hand,  the  pn)portion  of  salts  is  reduced  where  great 
rivers  empty  into-the  sea  or  where  great  bodies  of  ice  melt. 

'  Evaporate  a  >mall  portion  of  sea  water  until  it  is  very  much  concentrated. 
Then  warm  a  drop  of  this  concentrated  fluid  on  a  piece  of  glass,  and  put  it  instantly 
under  a  microscope.  You  will  see  ihe  saline  sulistances,  which  have  given  the  sea 
water  its  peculiar  taste,  crystallizing  in  regular  shapes,  as  the  water  gradually  dries 
from  the  glass. 

171 

\ 


1/2 


THE   SEA    AND   THE   OCEANS 


Saltness  of  partly  Inclosed  Bodies  of  Water. — Theoretically, 
owing  to  excessive  evaporation,  the  waters  of  the  Mediterranean 
Sea  ought  to  contain  a  greater  proportion  of  saline  matter  than 
the  adjacent  Atlantic,  and  such  is  said  to  be  the  case  off  the 
coast  of  Tripoli,  where  they  are  subject  to  rapid  evaporation  by 
the  hot  winds  from  the  Libyan  desert. 

In  the  Red  Sea,  too,  there  is  a  concentration  of  saline  matter. 
No  streams  of  any  consequence  flow  into  it,  and,  almost  com- 
pletely landlocked,  it  is  subject  to  excessive  evaporation;  so  that 

it  exhibits  a  degree  of 
saltiness  found  only 
in  some  salt  lakes. 

In  higher  latitudes, 
where  the  evapora- 
tion is  not  so  great, 
and  where  there  is  a 
large  inflow  of  ter- 
restrial water,  land- 
locked seas  are  less 
salt  than  the  adja- 
cent ocean.  Some 
parts  of  the  Baltic, 
for  instance,  are  al- 
most fresh. 

Color  of  the  Sea. — 
The  sea  is  green  or 
blue  ;  it  is  sometimes  colored  here  and  there  by  reddish,  or 
whitish,  yellowish,  or  crimson  patches,  according  to  the  tints 
imparted  by  the  color  of  the  bottom,  by  the  shadow  of  the 
clouds,  by  the  ingredients  of  its  waters,  or  by  its  myriads  of 
organisms.  In  certain  parts  of  the  Indian  Ocean  the  waters, 
as  seen  from  a  distance,  are  black. 

In  the  Mediterranean,  in  the  Gulf  Stream,  and  between  the 
tropics  generally,  the  sea  waters  are  dark  blue  ;  along  the  shores 
and  near  the  mouths  of  great  rivers  and  in  coral  seas  they  are 
green. 


Pho.sphoresceni'  Sea 


I'lK  iS^lloRESCKNTK 


/  5 


Thus  the  sea  assumes  here  and  there  various  shades  of  color; 
yet  its  waters,  when  viewed  by  the  tumblerful,  are  as  clear  as  the 
purest  crystal. 

Phosphorescence.  — In  most  parts  of  the  sea  the  water  is 
phosphorescent.  The  phosphorescence  is  caused  by  certain 
minute  living  bodies  which,  like  glowworms  and  fireflies  on  the 
land,  have  the  power  of  emitting  light,  some  in  flashes,  and 
some  in  a  steady  glow.  These  little  creatures,  invisible  to  the 
naked  eye,  are  as  multitudinous  as  the  sands  on  the  shore. 


In  .\kctic  IcK 
Breaking  out  of  Etah.    Peary  expedition.    From  Bulletin  of  the  Piiilarlelphia  Geographical 

Society. 

In  tropical  seas  and  in  certain  waters  they  tip  the  waves  with 
flame,  and  cover  the  sea  after  dark  with  sheets  of  light.  As  the 
ship  plows  these  waters,  she  leaves  a  bright  streak  far  behind 
in  her  wake. 

Though  we  cannot  see  the  dolpliin  and  other  fish,  as  they  s]iort  in  the 
depths  of  these  phosphorescent  seas,  yet,  by  the  streaks  they  leave  beliiiid. 


74 


THE   S1£A    AND   THE   OCEANS 


we  can  often  track  them  through  tlie  water,  as  we  do  rockets  t^hrough  the  air. 
As  they  chase  each  other  in  the  mazes  of  their  .sport,  these  threads  of  light 
are,  to  those  who  are  fortunate  enough  to  see  them,  among  the  most  pleasing 
wonders  of  the  deep.     They  are  particularly  beautiful  in  the  liarbor  of  Callao. 

The  Temperature  of  the  Sea  is  in  general  highest  near  the 
surface.  In  the  equatorial  waters  the  average  surface  tempera- 
ture is  about  80°  F.,  sometimes  rising  in  the  Indian  Ocean  to  90°, 
and  in  the  Red  Sea  to  94°.  Toward  the  bottom  the  tempera- 
ture is  depressed.  Indeed,  near  the  bottom  all  over  the  globe 
deep  sea  water  seems  to  be  about  as  cold  as  that  of  the  polar 
seas. 

During  the  Arctic  winter  the  sea  is  frozen  to  the  depth  of  several  feet,  form- 
ing floe  ice,  through  which,  by  the  action  of  the  tides,  currents,  and  winds, 
temporary  channels  or  leads  are  opened.  Taking  advantage  of  these  water 
ways,  the  explorer  or  navigator  urges  his  ship  onward.  Oftentimes,  however, 
the  channels  are  closed  with  prodigious  force  and  his  vessel  nipped  if  not 
crashed.  As  a  result  of  this  ice  movement  barriers  of  broken  or  pack  ice  are 
formed  which  may  reach  the  height  of  100  feet. 

The  Oceans.  —  The  sea  is  one  immense  body  of  water  encir- 
cling the  globe.  It  is,  however,  divided  by  the  intervening  land 
masses,  or  continents,  into  smaller  bodies,  called  occajis.  Of 
these  the  Pacific  is  the  largest.  It  contains  more  than  half  the 
water  of  the  sea.  Next  in  size,  but  only  about  half  as  large 
as  the  Pacific,  is  the  Atlantic.  The  Indian  is  the  third  in  area. 
The  Arctic  is  properly  only  an  extension  of  the  Atlantic,  while 
the  Antarctic  hardly  deserves  to  be  regarded  as  distinct  from  the 
main  body  of  the  sea. 

The  form  of  each  ocean  basin  depends  upon  the  shape  of  the 
inclosing  continents.  The  Pacific  approaches  the  oval  ;  the 
Atlantic  has  been  compared  to  a  long-  trough  ;  the  Indian  is 
triangular;  while  the  polar  oceans  are  very  irregular. 

Of  all  the  oceans  the  Atlantic  is  the  most  marked  by  inden- 
tations of  its  shores.  The  Asiatic  edges  of  the  Pacific  and 
Indian  oceans  are  also  well  supplied  with  bays  and  border 
seas. 

Depth  of  the  Oceans. — Two    questions    comiected    with    the 


Util'TH    OF    1  UK    (  K  IIANS 


175 


subject  ot  ocean  basins  have  been  made  matter  of  accurate 
in\'estigati(>n  —  their  depth  and  the  configuration  of  their 
bottom. 


so                               40     LONGITUDE       30          FROM           20    GREENWICH 

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\'K,KriC.\I.    SKi    riuN    1)1      1111     AllA.Nlli      (  )*  h.\-N    Al    52      NiiKIII     i,\lll,l<l. 

The  average  depth  of  the  Atlantic  is  about  12,000  feet.  It 
seldom  exceeds  18,000  feet,  or  3i  miles.  The  deepest  sound- 
ing has  been  made  70  miles  north  of  Porto  Rico.  It  was  27,366 
feet,  or  ratiier  more  than  five  miles. 

The  Pacific  has  a  somewhat  greater  average  depth  than  the 
.\tlantic.  Like  the  Atlantic,  it  has  deep  abysses.  Soundings 
of   27,930  feet  have  been  made  in  a  large   depression,  known  as 


Vertical  Section  ok  ihe  An.AN'ric  Ocean  at  14°  48'  Xoriii  J^atitupe 

Tuscai'flra  deep,  east  of  northern  Japan  and  the  Kurile  Islands, 
and  one  of  30,930  in  Lat.  30°  27'  7"  S.,  Long.  176°  39'  W.  The 
greatest  depth  known,  however,  3 1,614  feet,  is  near  the  island  of 
Guam,  a  southern  member  of  the  Ladrone  group. 

The  Bottom  of  the  Ocean  is,  like  the  land,  diversified  with  hill 
and  dale.  \^ast  plateaus,  banks,  and  shoals  spread  themselves 
out;  and  islands  rise  from  the  ocean  depths  far  more  abruptly 
than  mountains  do  from  the  lowlands. 

Haiti  and  many  other  islands  of  the  sea  rise  precipitouslv 
from  the  bottom  to  the  surface.  The  Silla  de  Caracas,  on  the 
other  hand,  which  is  the  steepest  mountain  in  the  world,  rises 
at  an  angle  of  53°. 

The  bed  of  the  Atlantic  has  been  more  thoroughly  examined 
than  any  other.      It    seems  to    consist    of    two    nearly  parallel 

.M.-S.  I'HVS.  GEt  )C;. 1 1 


\y6  THK    SEA    AND    THK    OCEANS 

valleys  extending  north  and  south  and  separated  by  a  lofty 
dividing  ridge.  The  islands  which  are  scattered  along  its 
length  are  the  summits  of  this  ridge.  That  portion  of  the 
Atlantic  bed  to  which  the  name  of  Telegraphic  Plateau  has 
long  been  given  is  of  special  interest.  This  plateau  stretches 
entirely  across  from  Newfoundland  to  Ireland,  at  an  average 
depth  of  somewhat  less  than  two  miles. 

If  we  imagine  ourselves  walking  across  it  from  Newfoundland  to  Ireland, 
we  shall  first  descend  by  an  easy  slope  to  the  Grand  Banks.  Here  the  depth 
is  about  looo  feet.  Leaving  the  Grand  Banks,  we  shall  pass  quite  rapidly  to 
the  depth  of  about  13,800  feet.  From  this  point  there  is  not  much  variation 
in  the  depth  for  about  halfway  across  the  ocean.  When,  however,  we  have 
performed  half  our  journey,  we  shall  ascend  again,  first  rapidly  and  tlien 
gently,  until  we  reach  the  neighborhood  of  the  British  Isles.  For  a  distance 
of  about  230  miles  westward  of  Ireland  the  upward  slope  is  very  gradual  until 
we  gain  the  dry  land. 

Note.  —  The  practical  value  of  the  in  format  on  derived  from  the  Atlantic  deep-sea 
soundings  was  early  appreciated  by  Maury.  Almost  as  soon  as  the  results  of  the 
soundings  were  made  known  to  him,  he  saw  that  the  laying  of  a  telegraphic  cable 
was  a  practicable  project.  He  was  the  first  to  suggest  and  urge  the  carrying  out  of 
this  scheme,  the  accomplishment  of  which  has  been  one  of  the  grandest  achieve- 
ments of  modern  science.  To  Maury  belongs  the  glory  of  having  pointed  out  a  high- 
way under  the  waters,  whereby  the  ends  of  the  world  have  been  brought  into 
instantaneous  communication. 

Marine  Deposits  may  be  classed  as  marginal  ?lwA  abyssal. 

To  the  first  group  belong  the  silt  and  sand  brought  down  by 
rivers,  the  waste  of  the  continental  borders,  and  the  ooze  result- 
ing from  the  wear  of  rocks  by  glacial  action.  To  these  materials 
must  also  be  added  fragments  of  the  solid  parts  of  marine  ani- 
mals, especially  the  shells  of  mollusks.  The  average  width  of 
marginal  deposits  is  about  1 50  miles,  although  in  some  regions, 
as  off  the  mouth  of  the  Amazon,  they  may  reach  350  or  400 
miles.  Deposits  similar  to  those  here  mentioned  are  found  in 
inland  seas. 

Abyssal  deposits  are  spread  over  the  bottom  of  the  deep  sea. 
While  largely  of  volcanic  origin,  as  shown  by  microscopic  exam- 
ination, they  exist  also  in  the  form  of  ooze  of  organic  origin. 
Deposits  of  the  sea,  like  those  of  the  land,  are  chemically  modi- 


1/8  THE    SKA    AND   THE   OCEANS 

fied  and  take  on  characteristic  forms.  Of  the  abyssal  deposits 
red  clay  is  the  most  widely  distributed.  Its  volcanic  origin  is 
shown  by  the  presence  of  pumice  and  other  igneous  matter. 
Associated  with  the  red  clay  are  found  the  calcareous  and  silicious 
coverings  of  minute  marine  organisms.  Within  certain  areas 
they  occur  in  such  abundance  as  to  form  a  distinct  ooze ;  thus 
the  accumulation  of  certain  foraminifer  shells,  belonging  to  the 
Globigcriiia,  may  give  rise  to  globigcritia  ooze,  a  limy  or  cal- 
careous mass,  which  is  represented  in  the  earth's  crust  by  chalk. 
Again,  the  great  abundance  of  Radiolaria  shells  may  give  rise 
to  a  siiicioHs  ooze.  Near  the  south  pole  there  is  a  rather  large 
area  covered  with  a  silicious  ooze  which  has  resulted  from  the 
accumulation  of  the  hard  parts,  or  coverings,  of  low  forms  of 
plants  known  as  Diatoms.  The  distribution  of  the  various  marine 
deposits,  including  the  coral  sands  and  muds,  is  shown  on  the 
preceding  page. 


XVII.    WAVES.  TIDES.  AND   CURRENTS 


Waves.  "  "The  troubled  sea  that  cannot  rest  "  has  ever  been 
llic  emblem  of  unending  movement.  Waves,  tides,  and  cur- 
rents incessantly  disturb  it. 

Waves  are  caused  by  the  wind  which  strikes  upon  the  sur- 
face of  the  sea.  and  thus  produces  an  alternate  downward  and 


Breakers  api-roachim;  the  Shori 
Coronado  Reach,  San  Diego,  California.     Point  l,on>a  on  the  riglit. 

upward  movement  of  its  waters.  A  mass  of  water  moved  in 
this  way  is  called  a  wai'r.  The  elevated  portion  of  the  water 
is  called  the  crcs/ ;  the  distance  from  one  crest  to  another  is 
the  breadth  ;  the  depression  between  two  crests  is  called  the 
trongJi. 

'79 


i8o 


\VA\1.;S,    IIDKS,   AM)    CLKI-IKMS 


The  rolling  in  of  waves  upon  the  beach  produces  the  impres- 
sion that  the  entire  body  of  water  is  moving  toward  the  land. 
As  we  shall  see,  however,  when  we  come  to  consider  the  sub- 
ject of  tides,  it  may  actually  be  receding.  We  must,  there- 
fore, distinguish  between  the  motion  of  the  waves  and  the 
motion  of  the  water. 

If  we  produce  a  ripple  upon  the  surface  of  water  in  a  basin,  bath, 
or  pond,  the  ripple  will  travel  from  edge  to  edge  of  the  water,  and 
communicate  an  undulating  or  wave  movement  to  each  portion 
of  the  surface.    But  the  water  itself  has  no  progressive  movement. 


BKEAKKKS    U.N    THE   SHORE 

Coionado  Beach,  California.     Point  Lomaon  the  right.     From  ]5hotograph  l)y  H.  R.  Fitcli. 

The  action  of  a  breeze  upon  a  field  of  wheat,  or  tall  grass, 
illustrates  the  matter  very  forcibly.  The  wind  passes  over  the 
field,  and  each  stalk  and  blade  bends  alternately  down  and  up, 
thus  forming  depressions  and  wave  crests.  Yet  there  is  no 
onward  movement  of  the  stalks. 

Those  portions  of  the  water,  tiowever,  which  actually  reach  the 
shore,  do  possess  an  onward  movement.  Instead  of  being  driven 
against  an  adjoining  mass  of  water,  they  encounter  the  solid 
bottom.  Thus  the  lower  part  of  their  mass  is  retarded,  while  the 
upper  part  moves  onward,  curls,  and  dashes  as  a  dn^aker  upon 
the  beach. 

The  Height  of  Waves  depends  mainly  upon  the  force  of  the 
wind  and  the  depth  of  the  water.     In  general  they  are  not  more 


Tin;    VELOCITY   OF   WAVE   MOVEMENTS 


i8i 


than  8  or  lo  feet  high.  The  highest  known  are  those  off  the 
Cape  of  Good  Hope,  where  they  are  said  to  attain  the  height  of 
more  than  40  feet. 

The  bell  of  a  lighthouse  on  one  of  the  Scilly  Islands,  east  of  Lands  End. 
was  wrenched  off  by  a  breaker,  at  the  height  of  100  feet. 

The  Velocity  of  Wave  Movements  depends  ( i )  on  the  velocity 
and  force  of  the  wind  ;  and  (2)  upon  the  depth  of  the  water  and 
its  freedom  from  obstructions.     In  the  open  sea  the  advance  of 


\\'AVK  Action  on  Partly  Submerged  Rocks,  San  Diego  Couniy,  California 
From  photograph  by  H.  R.  Fitch. 

a  wave  movement  is  more  rapid  than  in  one  obstructed  with 
islands.  The  rate  of  ordinary  wave  travel  is  from  1 5  to  upwards 
of  50  miles  an  hour. 

The  wave  movements  of  the  ocean  are  incessant.  Even  where 
a  perfect  calm  prevails,  there  is  a  ceaseless  movement  of  the 
water,  which,  like  a  great  pulse,  keeps  the  surface  constantly 
rising  and  falling.  This  heaving  is  commonly  known  as  the 
ground  swell  of  the  ocean. 

Waves  affect  the  surface  chiefly.  The  highest  waves  in  a 
storm  have  no  appreciable  effect  in   water  more  than  a  quarter 


182 


WAVES,  TIDES,   AND   CURRENTS 


of  a  mile  in  depth.  A  wave  40  feet  high  and  a  quarter  of  a 
mile  in  breadth  would  not,  in  all  probability,  disturb  the  smallest 
grain  of  sand  lying  on  the  sea  bed  at  a  depth  of  200  fathoms. 
Force  and  Work  of  the  Waves.  —  The  heaviest  billows  beat 
against  the  shore  with  enormous  force.  They  undermine  and 
level  cliffs,  they  dash  great  rocks  to  pieces  and  grind  the  frag- 
ments into  gravel  and  sand  which,  distributed  along  the  shore, 
form  the  beach.     Sand  is  the  common  beach  material,  though  in 


\\A\  K    A<    riDN 


k\    111' Aiii  AMI.  1,\   JuLLA,  San    DiEi;o  Cuuntv,  Cali- 
fornia 


Note  also  the  sandy  beach  in  the  foreground  and  the  high  surf  in  the  center  of  the  picture 
where  the  waves  strike  the  submerged  rocks.     From  photograph  by  H.  R.  Fitch. 

times  of  storm  bowlders  may  be  thrown  up  by  the  waves  or 
broken  down  from  cHffs  and  headlands.  The  shore  has  often 
been  likened  to  a  mill  where  the  grinding  of  rocks  into  sand  is 
a  ceaseless  operation. 

Under  the  influence  of  waves  beaches  may  be  extended  into 
spits  or  points,  and  sand  thrown  up  as  barrier  islands.  The  lat- 
ter are  especially  well  illustrated  by  the  long,  narrow  sand  bar- 
riers of  the  Gulf  coast  of  Texas. 

Under  certain  conditions  waves  also  act  as  transporting  agents. 
The  presence  of  silicious  sand  on  the  lower  coast  of  Florida, 
where  the  rocks  are  coralline  limestone,  is  thus  accounted  for. 


lilt   TIDES 


l8- 


The  Tides  are  great  vvavelike  movements.  They  differ  from 
wind  waves,  (i )  in  their  extent ;  (2)  in  their  regularity  ;  (3)  in  their 
cause.  In  a  general  way  it  may  be  said  that  two  large  waves, 
each  having  its  crest  and  its  depression,  together  encircle  the 
globe  from  north  to  south.  These  two  ceaselessly  chase  each  other 
over  the  broad  expanse  of  the  sea,  occasioning  two  elevations  and 
two  depressions  of  its  waters  in  the  course  of  about  25  hours.^ 
From  the  fact  that  these  elevations  and  depressions  occur  with 
regularity  about  one  hour  later  each  day,  and  thus  rudely  mark 
the  time,  they  are  called  tides,  from  the  Anglo-Saxon  tid,  time. 


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The  elevation  or  rising  of  the  water  is  called  high  ox  flood  tide ; 
its  depression  or  falling,  loiv  or  ebb  tide.  These  occur  alternately 
every  six  hours. 

Cause  of  Tides.  —  The  tides  are  mainly  due  to  the  influence 
of  the  moon.  The  sun  also  has  a  tide-producing  power,  but  it 
is  insignificant  compared  to  that  of  the  moon,  owing  to  the  fact 
that. the  sun  is  400  times  farther  off. 

The  moon  is  comparatively  near  the  earth.  Let  us  sec  then 
how,  in  consequence  of  this,  she  affects  its  waters.  The  earth 
and  moon  may  be  regarded  as  two  bodies  revolving  about  a  com- 
mon center  of  gravity  c,  which,  owing  to  the  greater  mass  of 
the  earth,  as  compared  with  that  of  the  moon,  lies    1000  miles 

^  The  exact  time  is  24  hours  52  minutes,  or  what  is  known  as  a  lunar  clay,  the  time 
between  the  crossing  of  the  meridian  of  a  place  by  the  moon  and  her  appearance 
on  the  same  meridian  ngain. 


1 84 


WAVKS,   TIDKS,    AND   CURRENTS 


within  its  circumference.  The  two  bodies  are  exactly  balanced 
at  their  centers,  but  the  surface  of  the  earth  at  B  is  7000  miles 
from  the  common  point  about  which  the  earth  and  moon  revolve, 
in  consequence  of  which  there  is  developed  a  throwing  off  or 
centrifugal  force,  known  to  every  schoolboy  who  has  used  a 
sHng  or  whirled  a  bucket  of  water  over  his  head,  which   partly 


High  Tide  at  Ostend,  Belgium 

Ostend  is  noted  us  a  pleasure  resort,  its  Ijeach  affording  excellent  opportunities  for  bathing. 
In  front  of  the  buildings  is  a  protecting  wall.  The  hill-like  elevations  at  the  right  are 
dunes. 

overcomes  the  force  of  gravity  and  permits  the  outward  bulging 
of  the  water  in  the  form  of  a  tidal  wave.  At  A,  however,  in 
addition  to  the  slight  centrifugal  tendency  resulting  from  the 
movement  about  T,  the  tidal  wave  is  generated  by  the  direct 
attraction  or  pull  of  the  moon. 

Halfway  between  the  tidal  wave  crests  or  high  tides,  there 
are  depressions,  as  represented  in  the  illustration.  These 
occur  where  the  water  is  drawn  away  to  form   the  high   tides. 


CAl'SK   OK  'IIDKS 


.85 


They  create  the  low  tides.  Like  the  high  tides,  they  take 
place  twice  in  a  lunar  day,  at  intervals  of  a  little  more  than  12 
hours. 

Evidence  that  the  moon  chietiy  is  concerned  in  causing  the  tides 
is  found  in  the  fact  that  high  tide  at  any  place  occurs  nearly 
at  the  time  when  the  moon  is  over  the  meridian  of  that  place. 


l\l>E   Al    (JSlt.Mi.    IlKl.CII   M 


The  receding  waters  liave  left  a  broad  beach,  now  thronged  with  visitors.       In  ihe  back- 
ground at  the  left,  standing  high  above  the  water,  is  seen  the  landing  pier. 


A  marked  phenomenon  of  the  tides  is  that  the  intensity  of  the 
movement  varies.  Three  days  after  full  and  new  moon  the  flow 
or  rise  of  the  water  is  far  greater  than  usual.  This  is  explained 
by  the  fact  that  when  the  moon  is  new,  as  in  the  illustration  on 
page  183,  and  when  she  is  full,  the  sun  and  moon  combine  their 
tide-producing  forces,  forming  what  are  known  as  "the  spring 
tides.  During  these  the  flow  is  at  its  maximum.  When,  on  the 
other  hand,  the  moon  is  entering    her  second   and  her  fourth 


i86 


MOVKMENT   OF    IHE   TIDAL    WAV?:  1 87 

quarters,  the  two  forces  do  not  act  in  harmony,  and  as  a  con- 
sequence the  neap  tides  result,  in  which  the  height  is  much  less 
than  in  the  spring  tides. 

Movement  of  the  Tidal  Wave.  —  Were  it  not  for  the  interfer- 
ence of  the  continents  and  the  variations  in  the  depth  of  the 
sea,  a  tidal  wave  might  be  expected  to  follow  the  apparent 
course  of  the  moon  about  the  earth.  Such  a  wave  would  then 
move  from  east  to  west  with  its  crest  extending  in  a  north-and- 
south  direction.  The  sea,  however,  is  divided  by  the  land  into 
great  oceanic  basins  of  varying  depths.  By  the  continents  the 
wave  is  deflected  from  its  course,  and  according  to  the  depth 
of  the  w^ater  its  velocity  is  increased  or  diminished,  being 
accelerated  in  the  deeper  water  and  retarded  in  the  shallower. 
The  movement  of  the  tidal  wave  is  shown  on  a  chart  by  means 
of  cotidal  lines  which  connect  all  places  having  high  water  at 
the  same  time.  They  therefore  represent  the  crest  of  the  tidal 
wave. 

Speed  of  Tidal  Wave.  —  Since  the  tides  follow  the  moon,  they 
have  to  travel  round  the  earth  from  east  to  west  in  the  same 
time  that  she  appears  to  revolve  round  it;  namely,  24  hours 
and  52  minutes.  The  tidal  wave,  therefore,  in  equatorial 
seas,  would,  if  it  were  unobstructed,  and  could  pursue  a  direct 
course,  travel  at  the  rate  of  1000  miles  an  hour. 

It  must  be  borne  in  mind,  liowever.  that  the  water  in  miciocean  has  only  an 
imperceptible  progressive  motion;  it  is  the  undulation,  not  the  water,  that 
travels  at  this  high  rate  of  speed. 

The  waving  grain,  as  it  bends  to  the  breeze,  causes  an  undulation  that 
travels  across  the  field  faster  than  you  can  run:  but  the  stalks  are  rooted ; 
thev  only  sway  backward  and  forward  to  the  breeze.  So  it  is  with  the  deep 
sea  and  its  swell. 

When,  however,  the  tidal  wave  comes  near  the  shores,  where 
the  water  is  shallow  and  confined,  a  change  occurs.  The  un- 
dulation is  retarded,  but  the  motion  of  the  water  is  vastly  in- 
creased, and  it  sweeps  as  a  current  along  the  continental  shores 
and  up  the  bays  and  rivers.  The  current  gains  in  speed  as  the 
tidal  wave  loses, 


i88 


WAVES,   TIDES,    AND   CURRENTS 


fi« 


^u. 


.&J 


\\ 


Is 


*L 


Ari.AiNTic  CoAsr  Timcii 
Mean  height,  in  feet. 


The  current  often  attains  unusual 
speed  in  passing  headlands,  and  then 
the  term  race  is  commonly  applied  to 
it.  Such  an  accelerated  current  moves 
from  six  to  eleven  miles  an  hour. 

Height  of  Tides.  —  In  the  middle  of 
the  Pacific  Ocean  the  rise  of  the  tide 
is  sometimes  less  than  a  foot ;  in  the 
Atlantic,  near  Saint  Helena,  about 
three  feet.  On  the  other  hand,  be- 
tween the  converging  shores  of  narrow 
seas  and  bays  the  water  is  sometimes 
heaped  up  to  the  height  of  from  25 
to  40,  and,  in  the  Bay  of  Fundy,  from 
50  to  60  feet. 

The  Mediterranean  and  the  Red  seas,  how- 
ever, with  their  narrow  entrances,  almost  cut 
off  the  tidal  wave,  so  that  in  both  the  ebb 
and  flow  are  very  slight.  The  greatest  rise 
in  the  Mediterranean  is  about  1.2  feet.  This 
seldom  occurs. 

In  the  Caribbean  Sea  and  Gulf  of  Mexico, 
likewise,  the  tides  are  rarely  three  feet. high, 
owing  probably  to  the  fact  that  these  sheets 
ot"  water  are  protected  from  the  tidal  wave  l)y 
the  West  Indies. 

Very  great  differences  exist  be- 
tween the  tides  at  various  points  of 
the  same  coast.  On  the  shores  of 
Florida  the  rise  is  not  more  than 
about  three  feet.  It  increases  as  we 
go  northward,  until  we  reach  the 
Bay  of  Fundy,  where  it  attains  its 
maximum. 

At  some  points  on  the  shores  of 
Great  Britain  there  are  tides  of  great 
height  and  strength,  while  at  others 


riDKS    ()!■     RIVERS;     BORES  1 89 

close  by,  the  rise  and  fall  are  barely  perceptible.  The  rise  and 
fall  at  Liverpool  are  28  feet;  in  the  ^Bristol  Channel,  40  feet; 
at  Wicklow,  on  the  opposite  Irish  coast,  only  2  or  3. 

To  account  for  these  differences  various  causes  may  be  sug- 
gested :  the  form  of  the  bottom,  the  projection  of  headlands, 
the  narrowing  of  channels  along  which  the  tidal  current  is 
forced,  and  the  position  of  those  channels  with  reference  to 
the  direction  of  the  tidal  wave. 

A  glance  at  the  map  shows,  for  example,  that  were  the  tidal 
wave  propagated  from  the  northeast  instead  of  the  southwest, 
the  Bay  of  Fundy  would  cease  to  have  remarkably  high  tides. 

The  peculiarities  of  a  sliore  are  sometimes  such  as  to  cause  a  complete 
sundering,  or  division  of  tlie  tidal  waters.  Two  currents  are  tluis  formed. 
In  some  cases  these  meet  again  after  their  division  and  give  rise  to  a  2(j/iirl- 
pool.  Charybdis  in  the  Straits  of  Messina,  and  the  Maelstrom  among  the 
Lotbden  Isles,  are  illustrations  of  this  phenomenon. 

Tides  of  Rivers  ;  Bores.  —  The  tides  of  some  rivers  present 
interesting  peculiarities. 

They  enter  certain  river  channels  with  extraordinary  velocity. 
People  crossing  the  dry  bed  of  the  river  Dee,  in  England,  are 
sometimes  overtaken  and  drowned  by  the  inrushing  water. 

The  case  of  the  Amazon  is  of  special  interest. 

The  tides  ascend  tliis  river  to  a  greater  distance  from  tixe  sea  than  in  any 
other  river  of  the  world.  They  are  felt  700  miles  up  slrea.r  •  and  the  sin- 
gular phenomenon  is  presented  of  there  being  several  tides  in  the  river  at 
the  same  time ;  for  before  the  flood  of  one  has  reached  the  end  of  its  700 
miles'  journey,  several  other  tidal  waves,  each  in  succession  bringing  high 
tide  with  it,  have  had  time  to  enter. 

A  tidal  wave  of  great  height  sometimes  enters  the  mouth  of 
a  river  and  ascends  its  channel  as  a  perpendicular  wall  of  water. 
Such  a  tidal  wave  is  known  as  a  bore.  Among  the  most  remark- 
able are  those  of  the  Hugli  at  Calcutta,  the  Garonne  in  France, 
the  Tsien-tang  in  China,  and  the  Amazon. 

At  certain  times  bores  12  to  15  feet  high  come  rushing  into  the  channel  of 
the   Amazon  on  the  top  of  the  tide.     Sometimes  as   many  as   five,  30  or  40 


c^.;>f.  -^su|^ace;guri 

__i . , 1 


laO      Longitude        20  West  'M  from  GO      Greenwich        30 


(190) 


(19") 


192  WAVES,   TIDES,   AND   CURRENTS 

miles  apart,  dash  up  the  river,  capsizing  small  craft  as  they  go  and  spreading 
consternation  among  the  watermen. 

The  bore  of  the  Tsien-tang  is  even  greater  than  that  of  the  Amazon.  It 
spans  the  river  with  a  feather-white  and  roaring  wall  of  water.  20  feet  high, 
and  travels  at  the  rate  of  eight  miles  an  hour. 

The  Currents  of  the  Sea.  — There  are  rivers  in  the  sea.  They 
are  of  such  magnitude  that  the  mightiest  streams  of  the  land 
are  rivulets  compared  to  them.  They  are  either  of  warm  or 
cold  water,  while  their  banks  and  beds  are  water  of  the  oppo- 
site temperature.  Fo-r  thousands  of  miles  they  move  through 
their  liquid  channels  unmixed  with  the  confining  waters.  These 
movements  are  called  currents. 

The  mariner  can  sometimes  detect  them  by  the  different 
color  of  their  stream,  while,  if  they  give  no  such  visible  sign  of 
their  existence,  he  can  trace  them  by  testing  their  temperature 
with  his  thermometer. 

Classification  and  Course  of  Currents.  —  The  chart  on  pages 
190,  191,  exhibits  a  general  view  of  the  horizontal  currents. 

( 1 )  There  is  an  Equatorial  Current  sweeping  from  east  to 
west  on  each  side  of  the  equator,  and  well-nigh  encircling  the 
globe ; 

(2)  There  is  a  slight  eastward  Counter  Current  not  far  from 
the  equator  ; 

(3)  There  are  Polar  Currents  setting  from  the  polar  regions 
toward  the  equator  ; 

(4)  There  are  Return  Currents  setting  from  the  equator 
toward  the  poles. 

The  chart  also  shows  that  as  in  the  case  of  the  tidal  wave,  so 
in  the  case  of  oceanic  currents,  the  shores  of  continents  and 
islands  have  marked  effect  in  modifying  their  normal  courses. 
These  are  also  modified  by  the  rotation  of  the  earth. 

If  two  trains  are  moving  on  parallel  tracks  in  the  same  direction  and  with 
the  same  speed,  an  object  thrown  or  a  ball  shot  "point  blank"  from  one  to 
the  other  inay  strike  the  point  aimed  at.  But  if  the  train  from  which  the  ball 
is  shot  be  going  35  miles  an  hour,  and  the  other  only  15,  the  ball  from  the 
first  will  strike  in  advance  of  the  point  aimed  at.     If  the  direction  of  the  trains 


CLKKKMS   (^F    11IL-;    A  11. Wilt"  193 

be  eastward,  then  the  ball  will  strike  a  certain  flislann-  to  the  east  of  tiie  point 
aimed  at. 

This  is  what  occurs  when  water  starts  from  the  eqiuUoi  toward  the  poles. 
It  rotates  toward  the  east  at  the  speed  of  1000  miles  an  hour.  Passing  to 
either  pole,  therefore,  it  has  a  hi<jher  speed  of  rotation  than  belongs  to  the 
latitudes  which  it  reaches,  and  hence  it  has  an  eastward  movement. 

If  now  we  suppo.se  the  ball  to  be  discharged  from  the  slower  train,  it  will 
obviouslv  fall  behind,  or  to  the  westward  of  the  point  aimed  at.  This  is  v\iiat 
occurs  when  water  starts  from  either  pole  to  the  equator.  It  has  the  sK)wer 
rotary  motion  of  the  pole,  and.  as  it  approaches  the  equator,  it  constantly 
enters  latitudes  which  have  a  higher  speed  of  rotation.  They  pa.ss  it  by.  and 
it  lags  to  the  westward. 

Hence  currents  moving  to  the  poles  deri\e  from  rotation  an  eastward  trend  : 
those  moving  to  the  equator,  a  westward. 

In  treating  of  oceanic  currents  it  is  important  to  observe  the  methods  of 
naming  them.  A  northeast  wind  comes  from  the  northeast,  a  northeast  cur- 
rent .^'w.*-  tiru'ard  the  northeast.  In  other  wt)rds,  while  the  winds  are  named 
according  to  the  points  from  which  they  blow,  currents  are  named  according 
ti)  the  quarter  toward  which  tliey  flow. 

Currents  of  the  Atlantic.  —  T/ic  Equatorial  C?irrent  crossing  this 
ocean  between  the  shores  of  Africa  and  South  America  strikes 
the  latter  continent  at  Cape  Saint  Roque.  Here  it  divides. 
One  portion  passes  southward,  following  the  coast  line  of  South 
America.  It  is  named  the  Brazil  Currcvt.  Its  waters,  reach- 
ing the  Antarctic  regions,  are  carried  back  with  the  polar  cur- 
rent which  sets  along  the  west  coast  of  Africa,  toward  the 
equator. 

The  other  portion  of  the  Equatorial  Current,  on  leaving  Cape 
Saint  Roque,  flows  northwestwardly.  It  is  divided  by  the  West 
Indies.  Its  main  section  enters  the  Caribbean  Sea  and  the 
Gulf  of  Mexico,  and  from  these  it  issues  through  the  Strait  of 
Florida  as  the  well-known  Gulf  Stream.  Its  westerly  set  in  the 
Caribbean  Sea  is  so  strong  that  near  the  shores  vessels  can 
scarcely  make  headway  against  it. 

Among  the  return  currents  which  carry  the  ocean  waters 
from  the  equator  to  the  poles,  the  Gulf  Stream  is  the  most  re- 
markable. Issuing  from  the  tropics,  this  current  crosses  the 
Atlantic  in  a  northeasterly  direction.  On  leaving  the  Strait  of 
Florida,  it  takes  a  course  nearly  parallel  to  our  Atlantic  sea 


194  WANKS,   TIDES,    AND    CURRENTS 

board.  Reaching  the  latitude  of  Newfoundland,  it  turns  more 
directly  eastward. 

Near  the  Azores  it  becomes  a  widely  expanded  drift  rather 
than  a  well-defined,  riverlike  current.  Here  it  divides.  One 
branch  passes  southward,  skirts  the  western  shores  of  southern 
Europe  and  Africa,  and  then,  veering  to  the  westward,  finds  its 
way  back  into  the  Equatorial  Current.  The  other  passes  on 
to  the  northeast,  bathes  the  shores  of  the  British  Isles  and 
northern  Europe,  and  enters  the  Arctic  basin. 

The  length  of  the  Gulf  Stream,  from  the  Gulf  to  the  Azores, 
is  about  3000  miles.  Its  breadth  in  the  Strait  of  Florida  is 
about  40  miles.  In  its  progress  it  constantly  increases  in 
breadth,  till,  in  the  middle  of  the  Atlantic,  it  is  120  miles  across. 
The  depth  is  about  2400  feet  near  the  straits.  This  dimin- 
ishes as  the  width  increases.  Off  Charleston  it  is  reduced  to 
1800  feet. 

In  volume  the  Gulf  Stream  exceeds  the  Mississippi  more 
than  1000  times. 

The  temperature  of  the  surface  waters  of  the  Gulf  Stream, 
as  they  pass  the  Strait  of  Florida,  is  sometimes  as  high  as  85°  F. 
It  is  a  river  of  warm  water,  and  retains  its  warmth  in  a  remark- 
able manner.  Off  Cape  Hatteras,  and  even  as  far  as  the  Grand 
Banks,  its  temperature  is  15°,  20°,  or  even  30°  higher  than  that 
of  the  atmosphere. 

The  storing  up  of  heat  begins,  no  doubt,  while  the  Gulf 
Stream  is  still  a  part  of  the  Equatorial  Current,  and  continues 
all  the  time  that  its  waters  are  exposed  to  the  tropical  sua, 
whether  in  the  Atlantic  Ocean,  the  Caribbean  Sea,  or  the  Gulf 
of  Mexico. 

From  the  Gulf  up  to  the  Carolina  coasts  the  waters  of  the 
Gulf  Stream  are  of  an  indigo-blue  color  ;  and  the  line  which 
marks  the  division  between  them  and  the  edge  of  the  inshore 
waters  is  sometimes  so  sharp  that  the  observer  can  distinguish 
when  one  half  of  the  vessel  is  in  the  Gulf  Stream  and  the  other 
is  in  the  cool  littoral  waters.  In  short,  the  line  of  demarcation 
is  so  well  defined  that  navigators  in  the  olden  times,  when  both 


(LK  RENTS    OK    II  IK    I'ACIKU'  195 

instruments  and  methods  for  detcrminini^;  longitude  at  sea  were 
rude,  were  accustomed  to  judge  of  their  position  by  it. 

So  much  heat  is  conveyed  by  this  stream  to  northern  latitudes, 
that  the  winter  climate  of  the  whole  western  face  of  Europe  is 
softened  and  tempered  by  the  winds  blowing  from  its  surface. 

The  ponds  of  the  Orkney  Isles,  though  bot-dering  on  the  parallel  of  60^ 
north,  owing  to  this  moderating  influence,  never  freeze;  and  the  harbor  of 
Hammerfest.  the  most  northerly  seaport  in  the  world,  in  latitude  70^  40',  is 
ilways  open. 

On  the  east  side  of  Greenland  and  through  Davis  Strait  cold 
polar  currents  come  from  the  Arctic  Ocean  to  replace  the  warm 
water  carried  northward  by  the  Gulf  Stream.  Off  the  southern 
point  of  Greenland  these  currents  unite  and  advance  as  far  as 
the  Grand  Banks. 

Here  one  portion  of  the  iniited  stream  sinks  below  the  warmer 
and  lighter  waters  of  the  Gulf  Stream,  and  pursues  its  course  to 
the  tropics  as  an  undercurrent.  The  other  portion  turns  south- 
west and  follows  closely  the  eastern  coast  of  North  America, 
keeping  between  the  shores  and  the  Gulf  Stream,  as  far  south 
as  Cape  Hatteras,  where  it  passes  under  the  Gulf  Stream  and 
continues  its  way  to  the  equatorial  regions  mainly  as  an  under- 
current. 

This  current  supplies  the  markets  of  New  England  with  the 
choicest  fish  of  the  sea,  and  gives  to  the  coast  of  Maine  its 
singularly  cool  summer  temperature. 

At  the  Grand  Banks  the  Arctic  Current  meets  the  Gulf  Stream,  and.  chilling 
the  vapor  wliich  rises  from  its  surface,  produces  the  dense  fogs  which  render 
this  part  of  the  ocean  so  dangerous  to  navigation. 

From  the  Antarctic,  as  from  the  Arctic  Ocean,  there  is  a 
constant  flow  of  icy  waters  into  the  Atlantic  basin.  The  South 
Atlantic  Current,  issuing  from  the  Antarctic  Ocean,  follows  the 
western  shore  of  Africa,  passes  northwestwardly,  and  contrib- 
utes to  form  the  Equatorial  Current  of  the  Atlantic. 

Currents  of  the  Pacific  have  a  general  resemblance  to  those  of 
the  Atlantic. 

M.-S.  PHVS.   GE<iG.  —  12 


196  WAVES,   nUKS,    AND    (  IKRENTS 

Ah  Equatorial  Citnrnt  starts  westward  from  that  portion  of 
the  ocean  lying  to  the  southwest  of  Mexico.  I.ikc  the  corre- 
sponding current  of  the  Atlantic  it  divides.  One  branch  passes 
to  the  southward.  Bathing  the  eastern  shore  of  Australia,  it  is 
called  the  liaxt  Australian  Current.  Between  Australia  and 
New  Zealand  it  blends  with  the  Antarctic  Drift. 

The  northern  branch  of  the  Equatorial  Current  pursues  a 
course  not  unlike  that  of  the  northern  branch  of  the  Equatorial 
Current  of  the  Atlantic.  Passing  the  Archipelago  off  the  south- 
east coast  of  Asia,  its  main  body  turns  northeastward,  and, 
sweeping  past  the  Japanese  Islands,  receives  from  them  its 
n2ime.,  Japan  Current.  The  natives  of  Japan  call  it,  from  the 
dark  blue  color  of  its  waters,  Kuro-Shiwo,  that  is,  Slack  Stream. 

The  Japan  Current  is  the  Gulf  Stream  of  the  Pacific.  Like 
that  stream,  it  has  the  twofold  ofifice  of  watercarrier  and  heat- 
bearer.  It  transfers  the  water  of  the  central  and  western  Pacific 
to  its  northern  and  eastern  portions  ;  and  with  its  warm  waters 
it  softens  the  climate  of  the  Aleutian  Islands,  and  of  the  north- 
west coast  of  America,  just  as  the  Gulf  Stream  does  that  of 
western  Europe. 

Passing  the  Aleutian  Islands,  the  main  volume  of  the  Japan  Current  receives 
the  name  of  the  Aleutian  or  IVorth  Pacific  Current,  and  takes  a  southeast- 
wardly  course.  Reaching  the  coast,  it  gives  to  southern  Alaska  its  enormous 
annual  rainfall  and  its  abundant  timber  growth  ;  it  waters  Washington  and 
Oregon ;  and  then,  veering  to  the  westward.  l:)ecomes  again  a  portion  of  the 
Equatorial  Current. 

A  Polar  Current,  passing  either  under  or  to  the  side  of  a 
current  which  enters  the  Arctic  through  Bering  Strait,  flows  into 
the  Pacific.  Its  course,  between  the  Japan  Current  and  the  east- 
ern shores  of  Asia,  is  like  that  of  the  polar  current  which  flows 
between  the  Gulf  Stream  and  the  shores  of  America,  and,  further- 
more, like  the  Labrador  Current,  it  teems  with  fish,  thereby 
vastly  increasing  the  capacity  of  China  and  Japan  to  sustain 
their  large  populations. 

From  the  Antarctic  a  broad  drift  flows  toward  the  equator> 
Off  Cape  Horn  it  divides.     One  branch  pa.sses  into  the  Atlantic  ; 


J 


CI  RK I. NTS    OK    TFIK    INDIAN    OCEAN  I97 

the  other,  the  Hionbouit  or  Peruvian  Currefit,  enters  the  Pacific. 
The  Humboldt  Current  carries  its  cool  Antarctic  waters  all 
aloni;-  the  west  coast  of  South  America  from  Patagonia  to  the 
(ialapagos  Islands.  These  waters,  when  they  touch  the  equator, 
are  still  too  cold  for  the  growth  of  the  coral  polyp.  Hence  the 
whole  western  coast  of  South  America  is  without  coral  reefs  or 
coral  foruiation  of  any  kind  ;  though  in  the  same  latitudes,  at 
a  distance  from  the  coast,  where  the  waters  are  warm,  coral 
thrives  in  the  greatest  abundance. 

Near  and  at  the  equator  the  Humboldt  Current  is  deflected 
to  the  westward  and  becomes  part  of  the  Equatorial  Current  of 
the  Pacific. 

Currents  of  the  Indian  Ocean.  —  The  Indian  Ocean  has  no 
such  well-defined  system  of  currents  as  the  Atlantic  and  Pacific. 
North  of  the  equator  the  direction  of  the  flow  is  determined  by 
the  monsoons.  South  of  the  equator  an  Equatorial  Current, 
emerging  from  the  East  Indian  Archipelago,  sweeps  to  the 
westward.  Reaching  Madagascar,  it  branches.  The  eastern 
fork  passes  to  the  southward  and  merges  with  the  Antarctic 
Drift.  The  western  flows  along  the  eastern  coast  of  Africa  as 
the  Mozambique  Current.  Leaving  the  Mozambique  Channel,  it 
becomes  the  Agullias  Current,  and  south  of  the  Cape  blends 
with  the  Antarctic  waters. 

A  brancli  of  the  Antarctic  Drift,  setting  to  the  northwestward,  and  becom- 
ing the  West  Australian  Current,  pours  its  icy  flow  into  the  Indian  Ocean. 

Causes  of  Oceanic  Circulation.  —  The  chief  causes  of  oceanic 
circulation  are  to  be  found  in  the  winds  which,  brushing  the  sur- 
face of  the  water,  give  ri.se  to  superficial  currents.  These,  fol- 
lowing the  direction  of  the  prevailing  winds,  are  further  modified 
by  the  shape  of  the  land  masses.  In  this  manner  there  arc 
formed  in  the  sea  five  great  eddies,  those  of  the  northern  hemi- 
sphere moving  in  a  clockwise  direction  ;  those  of  the  southern 
hemisphere  in  a  counter-clockwise  direction. 

The  trade  winds  blowing  incessantly  to  the  westward,  and 
meeting  over  the  equatorial  regions,  impart  to  the  waters  be- 


198  WAVES,   TIDKS,   AND   CURRENTS 

neath  them  a  gentle  but  continuous  westerly  movement,  hence 
the  Equatorial  Current,  while  farther  to  the  north  and  to  the 
south,  under  the  influence  of  the  prevailing  westerly  winds,  the 
currents  bear  to  the  eastward. 

In  those  parts  of  the  Indian  Ocean  that  are  within  the  mon- 
soon district  the  currents  are  controlled  by  the  monsoon  winds. 
For  six  months  they  flow  in  one  direction,  for  six  months  in 
the  other. 

Some  winds  produce  irregular  currents.  Such  effects  have 
been  observed  upon  rivers,  ponds,  or  canals,  in  piling  up  the 
water  on  one  side  or  at  one  end,  and  by  blowing  it  away  from 
the  other. 

In  great  storms  at  sea  the  winds  may  drive  the  water  before 
them  and  pile  it  up  above  its  usual  level. 

It  has  been  held  that  oceanic  circulation  is  largely  due  to 
differences  in  the  specific  gravity  ^  of  the  waters  in  various 
parts  of  the  sea.  That  it  does  exert  some  influence  seems 
probable,  especially  in  the  interchange  of  water  between  the 
equatorial  and  polar  regions. 

Sea  water  when  heated  expands.  A  given  volume  of  such 
heated  water,  if  it  contain  the  same  proportion  of  salts  as  an 
equal  volume  of  colder  salt  water,  will  weigh  less.  On  the 
other  hand,  when  sea  water  is  chilled,  it  contracts  and  becomes 
heavier. 

The  surface  temperature  of  sea  water  in  polar  seas  is  about 
35°  F;  in  equatorial,  about  80°.  This  difference  of  temperature 
is  permanent,  and  sufficient  to  produce  a  marked  variation  in  the 
sj^ecific  gravity  of  the  water  in  the  two  regions. 

Wherever  the  waters  in  one  part  of  the  sea  differ  in  specific 
gravity  from  the  waters  in  another  part,  no  matter, from  what 
cause  the  difference  may  arise,  or  how  great  may  be  the  distance 
between  two  such  parts  of  the  sea,  the  heavier  water  will  flow, 

'  Two  bodies  arc  said  to  differ  in  specilic  gravity  when  equal  volumes  of  the  two 
differ  in  weight.  A  gallon  of  salt  water,  for  example,  weighs  more  than  a  gallon  of 
freshwater.  A  jiint  of  water  weighs  about  a  pound;  a  pint  of  quicksilver  weighs 
about  thirteen  pounds.  ^  .. 


SAKCiASSU    SEAS  1 99 

by  the  shortest  and  easiest  route,  toward  the  lighter  ;  and  the 
lighter,  in  its  turn,  will  seek  the  place  whence  the  heavier  came. 

Sargasso  Seas.  —  An  interesting  evidence  of  the  circulation 
of  the  oceanic  waters  is  to  be  found  in  what  are  known  as  Sar- 
gasso Seas,  so-called  from  sarga::o,  the  Spanish  name  for  sea- 
weed. These  are  vast  collections  of  drifting  seaweed,  which 
gather  in  those  portions  of  the  different  oceans  which  are  most 
free  from  the  influence  of  currents. 

If  bits  of  cork  or  chips,  or  any  floating  substance,  be  put  into 
a  basin,  and  a  circular  motion  be  given  to  the  water,  all  the  light 
substances  will  be  found  crowding  together  near  the  center  of 
the  pool  where  there  is  the  least  motion.  Like  such  a  basin  is 
the  Atlantic  Ocean,  with  its  Equatorial  Current  and  its  Gulf 
Stream.     The  Sargasso  Sea  is  at  the  center  of  the  whirl. 

The  Sargasso  Sea  of  tlie  Atlantic  embraces  an  area  of  several  hundred 
thousand  square  miles  :  and  though  tiie  weeds  are  all  afloat  and  held  by  noth- 
ing, yet  the  Sargasso  remains  where  it  was  over  400  years  ago,  when  Columbus 
passed  through  it  on  his  first  voyage  to  America. 

During  Maury's  researches  connected  with  the  "  Physical  Geography  of  the 
Sea,"  the  existence  of  four  other  Sargassos  was  established  :  namely,  one  in 
the  Indian  Ocean,  two  in  the  Pacific,  and  another  in  the  Atlantic.  (See 
Chart,  pp.  190.  191.) 


PART    IV.  — THE    ATMOSPHERE 

XVIII.     PHYSICAL  PROPERTIES    OF  THE    ATMOS- 
PHERE 

The  Composition  of  the  Atmosphere.  — Wherever  we  go  on  the 
surface  of  the  earth  we  perceive  that  air  is  present.  If  we 
ascend  above  the  mountain  tops,  or  pierce  the  loftiest  clouds,  it 
is  still  with  us.     It  envelops  the  earth. 

The  entire  mass  of  the  air  is  commonly  spoken  of  as  the 
atmosphere.  It  is  transparent,  and,  unlike  water,  is  a  mixture  of 
gases  and  not  a  chemical  compound.  Its  chief  ingredients  are 
oxygen  and  nitrogen.  These  elements  are  present  in  the  pro- 
portion of  21  parts  by  weight  of  the  former  to  79  parts  by 
weight  of  the  latter,  or  approximately  i  to  4.  In  addition  there 
are  also  present  in  the  air  carbon  dioxide  in  small  amount,  and 
in  lesser  degree  the  rarer  gases  argon,  krypton,  and  helium. 
F"urthermore,  ordinary  air  contains  water  vapor  and  dust  in  vary- 
ing amounts  as  a  result  of  its  interaction  with  the  hydrosphere 
and  the  lithosphere. 

Not  only  does  oxygen  form  a  part  of  the  atmosphere,  hut  chemically 
combined  with  hydrogen  it  forms  watw.  and  in  combination  with  several  other 
elements  such  as  silicon,  carbon,  calcium,  and  aluminum  constitutes  the  outer 
portion  of  the  lithosphere.  O.xygen  is,  therefore,  the  most  widely  distributed 
of  all  the  chemical  elements.  It  is,  moreover,  the  vivifying  agent  of  the 
atmosphere,  being  essential  to  the  existence  of  living  things. 

Nitrogen,  of  which  the  atmosphere  is  largely  composed,  is  to  the  chemist 
•' inert" ;  that  is,  it  does  not  combine  strongly  with  other  elements.  In  this 
particular  it  is  the  opposite  of  oxygen  and  consequently  does  not  enter  con- 
spicuously into  the  formation  of  the  earth's  crust.  Its  function  in  the  atmos- 
phere seems  to  be  largely  that  of  a  diluting  agent,  thus  preventing  the  Xuo 
great  activity  of  the  oxygen. 

Carbon  dioxide,  though  normally  present   in    the   atmosphere  in   a   small 

200 


ORIGIN    OF   Till-:   ATMOSI'HKRK  20I 

amount,  is  essential  to  plant  life.  It  is  exhaled  by  most  forms  of  animal  life 
and  is  at  times  generated  in  great  abundance  in  volcanic  regions,  especiallv 
where  vulcanicity  is  dying  out.  in  large  amount  carbon  dioxide  is  suffocating 
rather  than  poisonous,  cutting  otf  the  supply  of  oxvgen  which  is  essential  to 
life. 

Invisible  water  vapor  is  another  substance  found  in  greater  or  less  quantitv 
in  the  atmosphere.  It  results  from  evaporation,  and  is  one  of  the  forms 
assumed  by  water  in  its  circulation.  When  chilled,  this  vapor  collects  in 
the  form  of  minute  drops,  forming  clouds,  and  upon  further  cooling,  may  be 
]Meci])itated  as  rain.  hail,  or  snow. 

Dust  is  one  of  the  most  common  impurities  of  the  atmosphere  ;  and  although 
usually  confined  to  the  layers  over  the  land  surfaces,  it  is  in  some  instances, 
as  after  certain  volcanic  eruptions  of  the  explosive  type,  wafted  for  long  distances 
in  the  upper  regions  of  air  and  even  far  over  the  sea.  Furtliermore.  it  mav 
be  held  in  meclianical  suspension,  if  sufficiently  fine,  for  a  long  period  —  it  mav' 
be  several  moiitlis.  A  heavy  rainfall  cleanses  the  atmosphere  by  washing  the 
mechanically  suspended  particles  from  it,  hence  in  arid  and  semiarid  regions 
the  air  is  more  heavily  charged  with  dust  than  elsewhere.  Dust,  it  will  be 
seen,  is  to  the  atmosphere  what  sediment  is  to  water.  The  agitation  of  the 
wind  pollutes  the  air  with  dust  just  as  the  stirring  of  the  bottom  of  a  pond 
pollutes  the  water  with  mud. 

From  what  has  laeen  stated  it  is  obvious  that  the  atmosphere  over  the  sea 
is  freest  from  contamination  by  solid  matter.  A  microscopic  examination  of 
dust  deposited  from  the  atmosphere  shows  it  to  be  composed  of  a  great 
variety  of  substances,  both  mineral  and  organic,  including  certain  disease- 
bearing  germs. 

Origin  of  the  Atmosphere.  —  If  the  earth  onVinated  in  the 
nuinner  set  forth  by  the  nebular  theory,  we  can  readily 
conceive  that  in  its  early  stages,  on  account  of  the  prevail- 
ing high  temperatures,  much  matter  now  in  the  form  of  solids 
and  liquids  was  in  a  vaporous  or  gaseous  state,  and  that,  as  a 
result  of  such  condition,  many  substances  were  included  in  the 
atmosphere  which  are  not  now  present.  It  may  be  conceived 
further  that  by  chemical  combination  and  by  condensation 
from  cooHng — processes  continued  through  a  long  period  of 
time —  the  atmosphere  would  become  much  reduced  in  volume 
and,  at  the  same  time,  simpler  in  composition.  It  is  especially 
noteworthy  that,  according  to  this  view,  the  primitive  atmos- 
phere must  have  contained  within  its  body  the  elements  of  the 


202 


PHYSICAL    PROPERTIES   OF  THE   ATMOSPHERE 


primeval  sea,  or  the  first  hydrosphere,  which  came  into  exist- 
ence as  a  condensation  from  it. 

On  the  other  hand,  it  is  held  by  the  advocates  of  the 
planetesimal  hypothesis  that  "  the  substances  of  the  atmosphere 
and    ocean    were    originally  a   part   of    the    planetesimals   and 

helped  to  form  the  earth's 
mass,"  and  that  they  were 
subsequently  forced  to  the 
surface  by  the  compression 
due  to  gravity  and  the  heat 
involved  in  that  process. 

Weight  of  the  Air  or  At- 
mospheric Pressure. — 
Though  a  gaseous  body,  the 
atmosphere  is  influenced  by 
gravity.  Air,  therefore,  has 
weight,  from  which  follows 
atmospheric  pressure.  The 
famous  Galileo  was  the  first 
to  point  this  out.  A  pump 
maker  wished  to  know  from 
him  .why  a  pump  would  not 
raise  water  from  a  well  which 
was  more  than  32  feet  deep. 
Galileo  concluded  that  it  was 
because  a  column  of  water 
32  feet  high  is  as  much  as 
the  weight  of  the  air  can 
balance. 

Everywhere  upon  land  and  sea  this  pressure  is  felt.  If  the 
atmosphere  were  undisturbed  and  of  the  same  density  through- 
out, or  if  it  were  of  a  uniformly  decreasing  density,  we  might 
expect  it  to  exert  upon  all  points  at  the  sea  level  the  same 
pressure.  And  this  it  practically  does,  notwithstanding  the 
fact  that  it  is  a  medium  subject  to  numerous  and,  at  times, 
sudden  disturbances  which  do  not  fail  to  manifest  themselves 


TOKKICKI.I.I'S    liXPKklMKM' 


THE   MERCURIAL   BAROMKIER 


in  pressure  variations.  The  average  atmospheric 
pressure  at  the  sea  level  is  14.74  pounds  (for  con- 
venience usually  stated  15  pounds)  to  the  square 
inch  of  surface,  a  pressure  exceeding  a  ton  to  the 
square  foot. 

The  Mercurial  Barometer.  —  This  is  an  instru- 
ment used  for  measuring  atmospheric  pressure. 
Its  construction  is  based  upon  a  well-known  ex- 
periment of  Torricelli,  a  celebrated  pupil  of  Galileo. 
He  filled  a  tube,  about  three  feet  in  length,  with 
mercury.  He  then  carefully  inverted  the  tube, 
covering  its  open  end  with  his  thumb,  until  in- 
serted in  a  vessel  of  mercury.  When  released  the 
mercury  fell  until  it  was  about  30  inches  in  height. 
This  column  was  sustained  by  the  weight  of  the  air. 

In  Green's  Standard  Barometer,  here  shown,  the 
glass  tube  containing  the  mercurial  column  is,  for 
protection,  inclosed  in  a  brass  case.  To  the  upper 
end  of  the  case  is  attached  a  ring  (A)  for  the  sus- 
pension of  the  instrument ;  to  the  lower  end  is 
appended,  by  means  of  a  flange  ( /: ),  the  cistern. 
Through  a  slot  (B)  in  the  case  the  top  of  the  mer- 
curial column  may  be  seen  (obscured  in  the  figure 
by  the  vernier  which  moves  in  the  slot)  and  its 
height  determined  by  a  scale  graduated  in  inches 
and  tenths  of  inches.  For  convenience  and  more 
accurate  reading  the  scale  is  provided  with  a 
vernier  moved  by  a  milled  head  (C).  As  mercury 
is  affected  by  heat,  the  reading  of  the  instrument 
must  be  corrected  for  various  temperatures,  hence 
a  thermometer  (D)  is  attached  to  the  case.  The 
cistern  consists  of  an  upper  portion  in  the  form  of 
a  glass  cylinder  through  which  the  surface  of  the 
mercury  and  the  lower  end  of  the  barometric  tube 
may  be  seen.  The  lower  portion  of  the  reservoir, 
also  protected  by  a  brass  case,  consists  of  a  wooden 


204  PHYSICAL   PROPERTIES   OF  THE   ATMOSPHERE 

receptacle  terminated  with  a  kid  bag  which  forms  the  bottom  of 
the  mercury-containing  vessel.  At  the  lower  extremity  of  the 
cistern  case  there  is  an  adjusting  screw,  worked  by  a  milled 
head  (F),  the  upper  end  of  which  presses  against  a  button  at- 
tached to  the  kid  bag.  When  the  button  is  pressed  up,  the 
capacity  of  the  cistern  is  diminished  ;  when  it  is  withdrawn,  the 
capacity  is  increased.  To  use  the  barometer  the  adjusting  screw 
should  be  raised  or  lowered  until  the  surface  of  the  mercury 
just  touches  the  end  of  the  ivory  peg  (*),  which  establishes  the 
zero  point  of  the  scale. 

Variations  in  Atmospheric  Pressure.  —  Variations  in  atmo.s- 
pheric  pressure  are  occasioned  by  changes  of  level  and  by 
changes  in  the  weight  of  the  air. 

( 1 )  Effect  of  CJiangc  of  Level.  —  In  ascending  a  mountain,  the 
explorer  passes  through  a  certain  proportion  of  the  atmosphere, 
and  is,  of  course,  relieved  from  a  portion  of  its  pressure.  For 
the  first  10,000  feet  of  ascent  the  barometer  falls  10  inches  —  an 
average  of  one  inch  to  every  1000  feet  of  ascent.  For  the 
second  10,000  feet  the  barometer  would  fall  about  6.7  inches,  the 
amount  of  its  fall  constantly  decreasing  as  he  ascends.  Mr. 
Glaisher  in  his  balloon  reached  a  height  of  37,000  feet,  and  then 
the  barometer  went  down  to  seven  inches. 

The  lowest  reading  of  the  barometer  ever  observed  upon  a 
mountain  was  13.3  inches,  at  an  elevation  of  22,079  ^^et,  on 
the  summit  of  Ibi-Gamin,  in  Tibet.  It  is  easy  to  see  that  the 
amount  of  fall  furnishes  a  means  of  measuring  heights  of  moun- 
tains, and  altitudes  to  which  balloons  ascend. 

An  interesting  consequence  arising  from  tlie  \veigl>t  of  the  atmosphere  is 
the  fact  that  the  l)oiling  point  is  lowered  at  high  elevations.  At  about  the 
level  of  the  sea,  water  boils  at  212^  F.  At  Quitt).  i  i.ooo  feet  high,  the  boiling 
point  is  194°.     On  the  top  of  Mont   Blanc,  nearly   16,000  feet  high,  it  is  180". 

This  results  from  the  diminished  pressure  to  which  water  is  subjected  at 
great  elevations.  It  has  the  inconvenient  effect  of  making  it  impossible  in 
such  situitions  to  cook  i^y  boiling. 

(2)  Effect  of  Change  in  Weight  of  the  Atmosphere.  —  A  fall  of 
barometer  occurs,  also,  when  the  column  of  air  above  any  area  be- 


i'i<(ii:Ai;i.i:  iii.K.iir  m    iiii     \i  .\u,)sriiKkK  205 

comes  lii;"htcr  than  usual.  This  takes  place  when  there  is  more 
than  the  ordinary  aim)unt  of  vapor  in  the  air;  because  vapor  is 
lighter  than  dry  air.  Consequently,  the  greater  the  projM^rtion 
of  vapor  in  the  air,  the  lighter  that  air  will  be.  A  Ion.'  barometer 
therefore  usually  indicates  a  moist,  rainy  atmosphere.  A  high 
baroDteter  indicates  that  the  atmosphere  is  heavy  ;  either  because 
it  is  dry  or  because  it  is  dense. 

The  density,  or  compactness,  of  the  air  of  course  diminishes 
with  the  height.  On  lofty  mountains  it  is  highly  rarefied, 
which  means  that  its  particles,  being  relieved  from  pressure,  are 
more  widely  separated  from    one  another   than  at   lower  levels. 

Persons  a.scendin,i(  to  great  elevations  sometimes  experience  a  singular 
(lifficultv.  The  walls  of  the  blood  vessels  burst,  and  there  is  a  flow  of 
l)lood  from  the  nose  and  ears. 

This  iiuil  de  iiiontai^m\  ov  ///<>// ///n///  snA'/ii'ss.  as,  the  French  call  it.  is  seldom 
feh  at  a  lower  level  than  16.000  feet,  and  balloon  ascents  have  been  made  to  a 
height  of  29.000  feet  before  any  serious  inconvenience  has  arisen  from  this  cau.se. 

Lines  drawn  through  places  whicli  have  the  same  barometric  pressure  at  any 
gi\en  time  are  called  /si>/>(irs.  from  tlie  Greek  I'sos.  equal,  and  /xrros.  weight. 

Probable  Height  of  the  Atmosphere.  —  The  height  of  the  atmos- 
phere has  not  yet  been  definitely  determined.  Calculations 
based  upon  the  decrease  of  atmospheric  pressure  for  increase  of 
altitude  seem  to  indicate  that  at  the  height  of  about  50  miles  the 
air  would  become  too  light  to  affect  the  barometer  appreciably. 
This  would  apparently  fix  the  outer  atmospheric  limit.  On  the 
other  hand,  there  is  reason  for  thinking  that  the  atmosphere  has 
a  height  much  exceeding  50  miles.  It  is  believed  that  meteors  be- 
come visible  only  after  entering  the  atmosphere.  Observations 
made  upon  the  same  meteor  from  different  points  afford  data 
for  the  calculation  of  its  height.  But  since  the  meteor  is  luminous, 
this  height  must  represent  a  distance  within  the  atmosphere. 
From  calculations  of  this  character  it  is  now  thought  that  the 
atmosphere  may  even  exceed  100  miles  in  height.  While  in 
its  outer  layers  the  atmosphere  must  exist  in  an  extremely  rare- 
fied state,  there  is  the  possibility  that  some  of  its  rarer  elements 
may  exceed  the  greater  limit  given  above. 


206  PHYSICAL    PROPERTIES    Ol-    THE    ATMOSPHERE 

Atmospheric  Temperature.  —  The  process  by  which  the  air  is 
warmed  is  complicated  and  for  that  reason  can  be  best  understood 
by  the  separate  consideration  of  each  step. 

(i)  A  portion  of  the  radiant  heat  emitted  by  the  sun  is  inter- 
cepted by  the  earth.  In  its  passage  through  the  atmosphere  a 
part  of  this  heat  is  absorbed,  thus  increasing  the  tcvipcraturc  of 
that  body. 

(2)  The  layer  of  air  resting  directly  upon  the  terrestrial  areas, 
which  have  become  heated  by  the  impingement  of  radiant  heat, 
are  warmed  by  contact  with  the  heated  surfaces  (conduction). 

(3)  The  lowest  stratum  of  air,  thus  warmed  and  expanded,  is 
crowded  from  its  position  and  borne  upward  by  the  settling  of 
the  cooler,  and  therefore  heavier,  air.  In  this  manner  currents 
are  established  (convection)  which  circulate  to  a  limited  height; 
that  is,  until  the  warm  ascending  air  is  cooled  to  the  temperature 
of  the  air  above  it. 

(4)  Of  the  radiant  heat  falling  upon  the  water  areas  a  large 
part  is  reflected,  and  passing  outward  through  the  atmosphere 
again  contributes  to  its  warming  by  partial  absorption.  This 
also  may  become  a  source  of  atmospheric  movement. 

( 5 )  On  the  other  hand,  while  the  land  areas  are  poor  reflectors, 
they  emit  radiant  heat  from  which,  as  it  passes  outward,  the  air 
exacts  a  contribution. 

(6)  In  the  heating  of  the  lower  atmosphere  the  absorption  of 
radiant  energy  by  the  dust  particles  plays  an  important  part. 
As  they  become  heated,  they  in  turn  heat  the  air  that  surrounds 
them. 

(7)  Another  .source  of  atmospheric  heat  which  must  be  taken 
into  consideration  is  the  absorption  of  heat  radiated  from  the 
earth  by  watery  vapor.  In  this  particular  watery  vapor  is  said 
to  be  more  efficient  than  any  other  atmospheric  ingredient. 
Clouds  act  as  a  protective  covering,  thus  preventing  the  too 
rapid  cooling  of  the  lower  atmospheric  layers  and  the  disas- 
trous results  that  would  arise  from  it. 

Temperature  of  the  Air  as  affected  by  Night.  —  It  is  during  the 
day  that  the  heat  effects  of   solar  energy  are  most  pronounced. 


SEASONAL   VARIATION   IN    TEMFERATURE  20/ 

At  night  the  heated  land  surfaces  are  cooled  by  radiation,  for 
like  other  good  absorbers,  they  readily  part  with  their  heat,  which 
radiated  outward  into  the  air  serves  in  part  to  prevent  its  too 
rapid  cooling.  As  the  land  cools,  the  adjacent  air  also  cools  by 
radiation  to  it,  and  the  layer  resting  directly  upon  the  ground  is 
further  cooled  by  contact  (conduction).  This  is  well  illustrated 
during  the  winter  season  when  the  warming  of  the  ground  in 
the  daytime  is  not  sufficient  to  prevent  its  freezing  at  night. 
Then  the  air  in  contact  with  the  frozen  surface  is  itself 
reduced  in  temperature. 

Water,  on  the  contrary,  is  a  good  reflector  of  solar  heat,  a  poor 
absorber,  and  likewise  a  poor  radiator.  The  little  warming  that 
takes  place  on  the  surface  of  the  oceanic  areas  is  not  readily  lost 
by  radiation,  in  consequence  of  which  there  is  not  the  reduction 
of  temperature  at  night  noticed  on  land  surfaces,  nor  is  the  air 
in  contact  with  the  water  so  thoroughly  chilled  by  conduction. 
Hence  it  follows  that  the  range  of  atmospheric  temperature  over 
the  water  is  not  so  great  as  over  the  land. 

Seasonal  Variation  in  Temperature.  —  The  temperature  of 
the  air  nearest  the  earth  also  varies  with  the  season,  being 
warmer  in  summer  and  cooler  in  winter  than  in  either  spring  or 
autumn. 

^"  The  amount  of  radiant  heat  received  by  any  portion  of  the 
earth's  surface  depends  upon  the  directness  of  the  solar  rays. 
When  they  fall  vertically  they  give  rise  to  the  greatest  heat 
effects  ;  as  their  inclination  increases  these  effects  diminish. 
At  the  time  of  the  vernal  equinox  the  direct  rays  fall  upon  the 
equator.  As  spring  merges  with  the  northern  summer  the  direct 
or  vertical  rays  fall  upon  portions  of  the  earth's  surface  succes- 
sively nearer  to  the  Tropic  of  Cancer  until  at  midsummer  xjune 
21)  their  northern  limit  is  reached,  after  which,  as  has  been 
already  explained  (see  p.  27),  their  recession  southward  begins. 
\  During  this  season  the  heat  received  by  the  earth  is  furthermore 
increased  by  the  long  exposure  due  to  the  lengthened  days.  In 
the  meantime  the  amount  of  heat  lost  by  radiation  during  the 
night  is  greatly  diminished,  owing  to  the  shortness  of  that  inter- 


208  PHYSICAL   I'ROPERriES   OF  THE   ATMOSPHERE 

val.  Thus  the  surface  warms  to  summer  temperature.  Under 
these  conditions,  without  diminishing  the  importance  of  other 
processes,  special  emphasis  must  be  placed  upon  the  heating  of 
the  lower  atmospheric  layers  by  their  contact  with  the  heated 
land  areas. 

Although  midsummer  is  June  21,  the  highest  temperatures  are 
usually  experienced  some  weeks  later.  This  is  due  to  the  fact 
that  the  earth,  warmed  in  excess  of  its  radiation,  is  still  receiving 
radiant  heat.  As  the  season  advances,  however,  on  account  of 
the  increased  inclination  of  the  solar  rays  and  the  shortening 
of  the  days,  high  temperatures  cannot  be  maintained,  hence  the 
earth  becomes  cooler.  This  and  the  attendant  phenomena  serve 
also  to  reduce  the  temperature  of  the  air. 

In  the  winter  season  the  radiation  from  the  earth  is  in  excess 
of  the  warming  due  to  the  sun's  energy.  The  earth  now  becomes 
chilled,  and  as  a  consequence  the  temperature  of  the  air  in  con- 
tact with  it  is  likewise  lowered.  Just  as  the  heat  of  summer 
comes  later  than  midsummer,  so  the  cold  of  winter  comes  later 
by  a  few  weeks  than  midwinter  (December  22). 

Instruments  used  for  Measuring  Temperature. — The  instru- 
ments used  for  measuring  the  hotness  or  temperature  of  the  air, 
as  well  as  that  of  other  bodies,  are  termed  tJicnnonieters.  The 
ordinary  forms  are  based  upon  the  expansion  and  contraction  of 
liquids  when  influenced  by  heat  or  cold.  Practically  the  liquids 
employed  are  limited  to  mercury  and  alcohol  —  to  the  former 
on  account  of  its  high  boiling  point  and  to  the  latter  on  account 
of  its  low  freezing  point.  In  the  less  common  metallic  ther- 
mometers the  measurement  is  made  through  the  unequal  expan- 
sion of  thin  strips  of  different  metals,  and  in  one  instrument,  at 
least,  through  a  combination  of  the  expansion  of  a  liquid  and 
the  elasticity  of  a  metal. 

Tlie  mercurial  thermometer  is  that  in  common  use.  It  consists  of  a  capil- 
lary glass  tube  having  at  one  end  a  bulb  or  reservoir.  In  the  process  of  manu- 
facture both  the  bulb  and  the  tube  are  filled  with  mercury  which  is  heated  to 
the  boiling  point.  The  tube  is  then  .sealed  When  cooled  the  mercury  wiU 
settle,  filling  the  l)ull)  and  a  part  of  the  tube. 


IXSTKUMEXTS    USED    VOR    MtASL'klXLi    I  K.Ml'KK.Vl  I  Ki:        209 

The  methods  of  graduating  the  mercurial  thermometer  or  making  t\.e  saile 
1)\  which  it  is  to  be  read,  are  as  follows  :  Two  points  are  selected  as  standards 
—  the  freezing  point  and  the  boiling  point  of  distilled  water,  the  latter  under 
the  pressure  of  one  atmosphere,  for  the  boiling  point  varies  according  to 
atmospheric  pressure.  These  standards  have  been  selected,  as  they  can  be 
easily  established  on  any  thermometer.  According  to  the  Fahrenheit  scale 
(marked  F.  or  Fahr.  on  the  thermometer)  the  freezing  point  has  been  arl)itrarilv 
placed  at  32^  and  the  boiling  at  212  .  from  which  it  follows  that  iSoMntervene 
between  the  two  standard  points.  .According  to  tlie  Centigrade  scale  (marked 
C.  on  the  thermometer),  which  is  simpler,  tiie  freezing  point  has  been  placed 
at  0°  and  the  boiling  point  at  100".  The  degrees  of  this  scale,  it  will  be  seen, 
are  larger  than  those  of  the  preceding,  the  relation  being  100  to  180.  These 
are  the  scales  in  common  use.  and  they  may  be  either  stamped  upon  the  ther- 
mometer case  or  etched  upon  the  glass  tul^e.  The  latter  plan  is  preferable 
and  is  pursued  in  graduating  the  best  instruments. 

Cheap  thermometers  are  useful  in  a  general  way,  but  accurate 
readings  should  not  be  expected  from  them.  Furthermore,  if 
trustworthy  results  are  to  be  obtained,  the  thermometer  must  be 
properly  located.  It  should  never  be  placed  where  the  air  will 
be  influenced  by  any  warming  body,  and  especially  should  it  be 
protected  from  the  direct  rays  of  the  sun.  If  possible,  it  ought 
to  be  hung  in  a  shelter,  raised  above  the  ground,  and  placed 
apart  from  buildings,  so  constructed  as  to  permit  the  ready  cir- 
culation of  the  air.  When  this  cannot  be  done,  the  shelter  may 
be  built  out  from  the  north  window  of  a  building,  if  in  other 
respects  the  location  is  desirable. 


XIX.    CLIMATE 

Weather  and  Climate.  —  The  atmospheric  conditions  prevail- 
ing at  a  place  during  a  given  time  —  a  day,  a  month,  or  even  a 
year  —  constitute  its  ivcatJier.  Within  this  term  are  included 
various  elements  ordinarily  perceptible  to  the  senses,  such  as 
temperature,  moisture  or  dryness,  clearness  or  cloudiness,  the 
presence  or  absence  of  wind.  Climate  is  more  comprehensive, 
as  it  includes  "  an  aggregate  of  weather  conditions  "  based  upon 
observations  extending  over  a  series  of  years.  The  longer  the 
periods  of  observation,  the  more  valuable  become  the  data  upon 
which  climate  is  established. 

The  chief  elements  of  climate  are  temperature  and  moisture, 
of  which  the  more  important  is  temperature. 

The  principal  causes  which  modify  temperature  are,  distance 
from  the  equator;  distance  from  the  sea;  prevailing  winds  and 
ocean  currents ;  and  height  above  the  sea  level. 

Distance  from  the  Equator.  —  The  first  and  most  apparent 
cause  of  the  differences  in  climate  is  the  distance  from  the 
equator.  This  has  two  effects:  As  the  distance  increases,  (i) 
the  average  annual  temperature  falls;  and  (2)  there  are  greater 
contrasts  between  summer  heat  and  winter  cold. 

As  the  area  within  the  tropics  receives  the  vertical  rays  of 
the  sun,  it  is  the  region  of  the  greatest  heat.  Between  the 
tropics  and  the  polar  circles  the  sun's  rays  fall  obliquely  and 
therefore  e.xert  a  feebler  power.  Within  the  polar  circles  the 
inclination  of  the  sun's  rays  is  greatest,  hence,  except  during  a 
brief  period  of  a  few  weeks,  excessive  cold  prevails. 

The  contrasts  between  summer  heat  and  winter  cold  are 
mainly  due  to  variations  in  the  length  of  the  day,  and  these 
depend  on  distance  from  the  equator.     Within  the  tropics  there 


DISTANCE   FROM   THE   SEA  211 

is  comparatively  little  difference  between  the  two  periods  of 
day  and  night  through  the  year.  Only  twice  in  the  year,  at  the 
equinoxes,  are  they  equal  for  other  parts  of  the  globe. 

As  the  sun  passes  northward  from  the  equator,  the  day 
lengthens  over  the  northern  hemisphere,  until,  within  the  Arctic 
circle,  the  sun  does  not  set  at  midsummer.  The  same  phenome- 
non occurs  in  the  southern  hemisphere,  after  the  sun  passes 
southward  of  the  equator. 

Since  there  is  very  little  difference  between  day  and  night  at 
the  equator,  the  temperature  within  the  tropics  is  nearly  uni- 
form throughout  the  year. 

North  and  south  of  the  tropics  there  are  important  differences 
between  day  and  night,  in  consequence  of  which  climatic  con- 
trasts are  found  in  all  regions  outside  of  the  tropics. 

Within  the  polar  circles  these  contrasts  are  at  their  maxi- 
mum. The  Arctic  summer,  strange  to  say,  is  exceedingly 
warm.  It  is  marked  by  a  rapidity  of  plant  growth  that  is 
marvelous.  In  a  few  weeks  crops  mature  which  require  twice 
that  length  of  time  in  latitudes  much  nearer  the  equator.  But, 
on  the  other  hand,  the  winter  cold  is  correspondingly  excessive. 

Distance  from  the  Sea.  —  In  certain  countries  climate  is 
affected  more  by  distance  from  the  sea  than  by  distance  from 
the  equator. 

The  climate  of  a  region  adjacent  to  the  sea  is  called  an  insular 
or  maritime  climate.  The  climate  of  a  region  remote  from  the 
sea  is  called  an  inland  or  continental  climate. 

Certain  causes  moderate  insular  climates. 

(i)  Water  absorbs  heat  much  more  slowly  than  the  land, 
and  therefore  remains,  in  hot  weather,  comparatively  cooler. 
Hence  the  summer  temperature  of  a  country  bordering  on  the 
sea  is  lowered. 

(2)  On  the  other  hand,  water  parts  with  its  heat  by  radiation 
much  more  slowly  than  the  land,  and  therefore  remains  in  cold 
weather  comparatively  warmer.  Hence  the  winter  of  a  mari- 
time country  is  moderated. 

(3)  Vapor  is  incessantly  rising  from  the  sea,  and,  being  con- 

M.-S.  PHYS.  GEOG.  —  1 3 


212  CLIMATE 

densed,  falls  as  rain  or  snow  upon  the  land,  and  this  liberates 
latent  heat. 

(4)  The  vapor  in  the  atmosphere  of  a  maritime  climate  pre- 
vents the  escape  of  heat.  It  acts  as  a  blanket.  A  familiar 
illustration  of  this  is  the  fact  that  frost  rarely  occurs  on  cloudy 
nights, 

(5)  Again,  the  process  of  evaporation  goes  on  more  rapidly 
in  hot  weather  than  in  cold,  and  this  has  the  effect  of  moderat- 
ing the  summer  heat  of  a  maritime  country. 

For  the  above  reasons,  insular  or  maritime  climates  are 
equable,  or  free  from  extremes. 

Inland  or  continental  climates  are  the  opposite  of  maritime. 
They  are  subject  to  great  extremes,  intense  heat  in  summer  and 
excessive  cold  in  winter. 

Two  reasons  may  be  assigned  for  this  :  — 

( 1 )  Countries  far  from  the  sea  are  without  its  cooling  influence 
upon  their  summer  heat,  and  they  have  no  reservoir  of  warmth 
to  compensate  for  their  rapid  radiation  of  heat  in  winter. 

The  continent  of  Asia  affords  the  most  striking  instances  of  the  excessive 
character  of  inland  climates.  The  Russian  army  advancing  toward  Khiva  in 
1839-40  experienced  vicissitudes  of  temperature  from  a  heat  of  over  100^  F. 
to  a  cold  of  45°  below  zero. 

At  Werchojansk,  eastern  Siberia,  the  culminating  point  of  excessive  climate 
in  all  the  world  is  reached.  The  extreme  temperature  of  90.4°  below  zero  has 
been  observed  there.  The  soil  is  permanently  frozen  to  the  depth  of  380  feet. 
In  the  month  of  June  the  Lena  is  free  from  ice;  the  surface  soil  has  thawed 
for  three  or  four  feet ;  and  the  warmth  of  the  short  summer  is  such  that  grain 
will  ripen  in  the  shallow  stratum  of  soil  above  the  frozen  mass.  The  mean 
temperature  of  July  at  Yakutsk  is  69°,  the  same  as  at  Paris. 

(2)  The  comparative  dryness  of  the  air  of  an  inland  region 
contributes  to  create  extremes.  This  is  strikingly  illustrated  by 
the  climate  of  the  Sahara.  The  air  there  is  perfectly  dry.  No 
vapor  hinders  the  reception  of  heat  by  day  or  its  loss  by  night. 
Travelers  who  have  suffered  from  intense  heat  during  the  day 
have  found  the  water  in  their  canteens  frozen  before  morning. 

Prevailing  Winds  and  Ocean  Currents.  —  The  climate  of  a 
country  is  also  greatly  modified  by  the  prevailing  winds  and  the 


HEIGHT    ABOVE   THE    SEA    LEVEL  213 

neighboring  ocean  currents.  If  the  prevailing  winds  come  from 
the  sea,  they  temper  the  extremes  of  heat  and  cold.  If  a  cold 
current  bathes  any  portion  of  the  shore,  it  lowers  the  tempera- 
ture ;  a  warm  current  raises  it. 

The  British  Isles  and  the  province  of  Labrador  are  the  same 
distance  from  the  equator,  and  in  many  parts  the  same  height 
above  the  sea.  Yet  such  is  the  difference  of  climate  between 
them,  that  Labrador  is  covered  with  snow  for  nine  or  ten 
months  every  year,  and  is  so  cold  as  to  be  almost  uninhabitable  ; 
while  in  England  the  ground  is  rarely  covered  with  snow,  and 
the  pastures  are  green  all  the  winter. 

Both  countries  are  in  the  regions  of  westerly  winds ;  but  in 
Labrador  they  come  from  the  land,  and  are  dry  and  cold ;  in 
England  they  come  from  the  sea,  and  are  laden  with  moisture 
and  warmth.  The  shores  of  Labrador  are  washed  by  a  cold 
Arctic  current ;  those  of  Great  Britain  by  the  w^arm  waters  of 
the  Gulf  Stream  and  Atlantic  Drift. 

The  climates  of  western  Europe,  from  North  Cape  to  the 
Strait  of  Gibraltar,  are  modified  by  the  sea  winds  and  the  in- 
fluence of  the  Drift. 

Norway  stretches  beyond  the  70th  degree  of  north  latitude ;  yet  the  west- 
erly winds  are  so  richly  laden  with  warmth  and  moisture  from  the  waters  of 
the  Drift  that  the  harbor  of  Hammerfest.  latitude  70^^40',  is  never  frozen,  even 
in  the  severest  winters.  But  cross  the  Scandinavian  mountains,  and  there  is 
encountered  at  once,  if  it  be  winter,  the  severest  cold.  In  this  short  distance  ' 
from  the  warm  waters  and  the  west  winds  of  the  Atlantic,  the  Russian  lakes 
and  rivers,  the  gulfs  and  bays  of  the  Baltic,  are  found  closed  to  navigation 
every  year  from  November  till  May. 

Climatic  conditions  similar  to  those  which  affect  the  western 
shores  of  Europe  are  found  upon  the  western  slopes  of  Oregon, 
British  Columbia,  and  Alaska.  Westerly  winds  prevail,  and 
they  are  laden  with  moisture  from  the  Pacific  Ocean.  The  result 
is  that  here,  as  in  Norway,  open  harbors  and  evergreen  hills 
are  found  in  the  high  latitudes  of  Alaska  and  other  parts  of  our 
northwest  coast. 

Height  above  the  Sea  Level.  —  Among  other  circumstances, 
climate  depends  upon  heii^ht  above  the  sea.     A  change  of  ele- 


160        180        160        140        120        100 


160        180        160        110         120        100        80         60         10 


("4) 


20         40         t>0         au  100        liO  110        IGO 


CO         80         lUO        120        IIU        160 


C2I5) 


2l6  CLIMAIE 

vation  of  a  few  thousand  feet  at  the  equator  produces  a  change 
of  temperature  as  great  as  would  be  experienced  in  sailing 
6000  miles  to  the  frozen  regions  of  the  poles. 

The  island  of  Cuba  and  the  Mexican  mountain  of  Orizaba 
are  in  the  same  latitude.  The  summit  of  the  mountain  is  cov- 
ered with  snow  all  the  year ;  the  island  with  fruits,  flowers,  and 
evergreens. 

The  reason  why  elevation  above  the  sea  level  causes  reduc- 
tion of  temperature  is  that  the  radiation  of  heat  goes  on  from 
elevated  parts  of  the  earth's  surface  more  freely  than  from  its 
lower  portions.  Two  causes  may  be  assigned  for  this  :  (i)  ele- 
vations are  comparatively  small,  and  therefore  have  a  smaller 
store  of  heat;  (2)  the  air  and  vapor  upon  elevations  are  rare- 
fied, and  hence  little  hindrance  to  radiation  is  presented. 

The  general  rule  as  to  the  effect  of  elevation  is  this :  for 
every  one  hundred  yards  of  perpendicular  ascent  there  is  a 
decrease  of  one  degree  in  the  temperature;  so  that,  even  at 
the  equator,  by  ascending  to  the  height  of  about  16,000  feet 
above  the  sea,  one  may  reach  the  snow  line. 

Isothermal  Lines.  —  From  thermometric  observations  made  in 
all  parts  of  the  world,  the  actual  distribution  of  temperature 
over  the  globe  has  been  ascertained.  To  show  this,  Humboldt 
constructed  a  series  of  lines  called  isotJiernis,  or  lines  of  equal 
heat.  These  are  drawn  round  the  globe  so  as  to  connect  all 
places  which  have  the  same  mean  temperature  during  the  year 
or  any  given  part  of  the  year. 

^\  Isothermal  lines  are  far  from  coinciding  with  the  parallels 
of  latitude.  Let  us  take  by  way  of  illustration  the  line  in  the 
northern  hemisphere  indicating  the  mean  annual  temperature 
of  50°.  (See  chart,  pp.  214,  215.)  It  passes  through  Oregon 
on  the  Pacific  shores,  and  leaves  the  Atlantic  coast  between 
New  York  and  New  Haven.  It  bends  northward  in  crossing 
the  Atlantic,  and  in  Europe  passes  near  Liverpool,  Vienna, 
and  Odessa,  and  in  Asia,  near  Pekin. 

The  summer  isotherms  cross  Great  Britain  as  east-and-west  h'nes.  The 
winter  isotherms  are  nearly  north-and-south  Hnes. 


ZONES  OF  TEMPERATURE  21 7 

We  are  not  to  conclude,  however,  that  because  the  same 
isothermal  line  passes  through  two  places,  they  have  a  climate 
identically  the  same.  Of  two  such  places  one  may  have  an 
extremely  hot  summer  and  a  correspondingly  cold  winter.  The 
other  may  have  a  climate  free  from  extremes.  Yet  both  may 
have  the  same  average  yearly  temperature. 

San  Francisco  and  Washington  have  the  same  mean  annual  temperature, 
while  their  climates  differ  greatly. 

Again,  the  same  isothermal  line  passes  through  New  York  and  Dul)lin. 
Yet  the  climates  of  these  places  have  no  resemblance.  The  mean  winter 
temperature  of  Dublin  is  6'  above  that  of  New  York ;  while  the  summers 
of  the  two  places  are  so  unlike,  that  whereas  grapes  and  Indian  corn  are 
successfully  cultivated  in  the  vicinity  of  New  York,  they  will  not  ripen  in 
tiie  open  air  at  Dublin. 

Zones  of  Temperature.  —  By  means  of  isotherms  we  define 
the  zones  of  temperature.  They  are  indicated  by  the  colors 
on  the  chart.  The  true  Torrid  Zone  is  bounded  by  the  iso- 
therms of  70°  on  either  side  of  the  equator.  The  true  Tem- 
perate Zones  extend  from  the  isotherms  of  70°  to  those  of  32° ; 
the  Frigid  Zones  from  these  to  the  poles. 


XX.     ATMOSPHERIC    CIRCULATION 


Winds.  —  A  body  of  air  in  motion  is  called  a  wind.  The 
rate  of  motion  and  the  direction  of  winds  vary  greatly.  By 
means  of  an  instrument  called  the  anemometer,  it  has  been  as- 
certained that  the  velocity  of  a  light  wind  is  5  miles  an  hour ; 

of  a  stiff  breeze,  25  miles;  of 
a  storm,  50  miles  ;  and  of  a 
hurricane,  80  to  100  miles,  or 
even  100  to  150  miles. 

Again,  the  direction  in 
which  winds  blow  is  so  con- 
stantly changing  that  they 
are  often  spoken  of  as  fickle, 
inconstant,  and  uncertain. 
There  is,  however,  order  in 
the  movements  of  the  atmos- 
phere. The  fickle  winds  are 
obedient  to  laws.  There  are 
causes  that  make  them  blow 
with  greater  or  less  rapidity ; 
there  are  reasons  why  they 
blow  now  north  or  south,  now 
east  or  west. 

Winds  are  named  according  to 
the  quarter  from  which  they  blow. 
A  west  wind  comes  from  the  west; 
an  east  wind  from  the  east. 


Anemometer 
This  instrument,  which  is  used  for  determin- 
ing the  velocity  of  the  wind,  is  placed  in 
an  unobstructed,  elevated  position,  as 
above  the  roof  of  a  high  building.  It 
consists  of  four  hollow  hemispherical 
cups  mounted  vertically  on  arms  which 
are  attached  to  a  vertical  axis.  The 
lower  portion  of  this  axis  communicates 
the  motion  of  the  rotating  cups,  by  means 
of  an  endless  screw,  to  a  series  of  dials 
which  register  the  number  of  revolutions. 


Cause  of  Winds. — The  chief 
cause  of  winds  is  the  unequal  distribution  of  heat  in  the  atmos- 
phere. The  underlying  principle  is  illustrated  by  the  following 
examples, 

218 


GENERAL   CIRCULATIOX   OF   THE   ATMOSPHERE  219 

If  a  fire  is  lighted  on  the  hearth,  the  air  within  the  chimney 
will  be  heated  and  forced  upward  by  an  indraught  of  cooler 
and  heavier  air  from  all  parts  of  the  room.  This  continues  as 
long  as  the  fire  burns. 

The  same  occurs  when  a  bonfire  is  lit,  or  a  house  is  on  fire. 
I'A'ery  child  knows  that  "  the  sparks  fly  upward  to  the  sky." 
They  are  carried  up  by  the  hot  ascending  currents.  The  air 
above  the  fire  is  expanded,  rendered  lighter,  and  driven  upward 
by  currents  of  cool  air  that  come  rushing  in  from  all  sides. 
These,  when  heated,  ascend  with  such  force  as  to  carry  up 
clouds  of  smoke  and  sparks. 

This  unequal  distribution  of  heat,  as  in  the  warming  of  the  air  within  the 
chimney  while  that  in  the  room  is  comparatively  cold,  establishes  a  system  of  air 
currents.  If  there  are  no  obstacles  in  the  way  and  if  these  currents  are  neither 
chilled  nor  heated  in  their  course,  they  will  go  straight  toward  the  mouth  of 
the  chimney.  Chairs  and  tables  as  well  as  other  objects  in  the  room  will 
deflect  them  and  cause  more  or  less  irregularity  in  their  direction. 

To  prove  that  such  currents  really  do  flow,  place  a  lighted  candle  in  the 
doorway  of  a  room  in  which  a  fire  is  burning.  The  flame  will  be  drawn 
inward  by  the  current. 

Now  what  occurs  in  the  air  of  a  room  w^hen  a  fire  is  kindled 
on  the  hearth  takes  place  in  the  atmosphere.  Some  portions 
of  it  are  always  more  heated  than  others  ;  and  the  unequal  distri- 
bution of  heat  establishes  a  system  of  currents.  The  heated 
surface  of  the  earth  warms  the  air  above  it.  This  air,  forced 
up  by  the  surrounding  cool  air,  ascends  as  a  current ;  and  streams 
of  cooler,  heavier  air  flow  in.  In  proportion  to  the  size  of  the 
area  heated,  the  volume  of  the  inflowing  currents  will  be  greater 
or  less,  and  in  proportion  to  the  difference  of  temperature 
between  the  heated  air  and  the  inflowing  currents,  the  rapidity 
of  their  flow  will  be  greater  or  less. 

General  Circulation  of  the  Atmosphere. — Turning  now  our 
attention  from  these  simple  illustrations  to  the  general  circulation 
of  the  atmosphere,  we  find  that  within  the  tropics  there  is  per- 
petual summer.  Here  the  air  is  heated  and  filled  with  watery 
vapor,  while  the  air  on  either  sidejs  co^l^and  comparatively  dry. 

liOS  HI^GBliES,  CRli. 


220 


ATMOSPHERIC  CIRCULATION 


What  must  be  the  effect  of  this  unequal  distribution  of  heat  and 
vapor  ?  There  can  be  but  one  answer :  it  creates  a  general 
circulation  of  the  atmosphere.  In  the  first  place,  as  in  the  case 
of  the  fire  upon  the  hearth,  the  heated,  moist  air  of  the  tropics 
is  pressed  upon  by  the  heavier  air  on  either  side.  It  is  forced 
upward,  and  there  is  an  indraught  both  from  the  north  and  the 
south  to  supply  its  place. 


Circulation  of  the  Atmosphere 


If  the  earth  were  at  rest,  and  if  its  surface  were  covered  with 
water,  the  inflowing  currents  would  go  straight  from  the  polar 
to  the  equatorial  regions.  ]  There  would  then  be  a  simple  circu- 
lation of  light  air  from  the  equator  to  the  poles,  and  of  heavy 
air  from  the  poles  to  the  equator.  The  winds  would  be  steady 
and  unvarying. 

But  the  earth  is  not  at  rest,  and  its  surface,  instead  of  being 
uniformly  covered  with  water,  is  varied  by  land  masses  of  greater 
or  less  magnitude  and  elevation.     The  rotation  of  the  earth  and 


CONSTANT   OR   TRADE   WINDS  221 

the  influence  of  its  land  masses  are  two  causes  which  largely 
affect  the  circulation  of  the  air  and  render  it  exceedingly  com- 
plicated. 

Winds  are  classified,  according  to  the  regularity  with  which 
they  blow,  as  cojistant,  variable,  and  periodical. 

Constant  or  Trade  Winds.  —  Certain  of  the  winds  blow  with- 
out interruption  in  the  same  direction  and  at  nearly  the  same 
rate.  So  constant  are  they  that  vessels  often  sail  in  them  for 
days  without,  as  the  sailors  say,  "  changing  a  stitch  of  canvas." 
It  was  the  steady  blowing  of  these  winds  which  so  alarmed  the 
crew  of  Columbus  on  his  first  voyage  to  America,  and  led  them 
to  fear  that  they  would  never  get  back  to  Europe.  From  their 
always  pursuing  one  trade,  i.e.  path,  or  from  their  importance 
to  navigators,  these  winds  have  been  called  trade  winds,  or  the 
trades. 

If  the  earth  had  no  daily  motion,  these  winds  would  blow  on 
one  side  of  the  equator  from  the  north;  on  the  other  side  from 
the  south  ;  and  in  both  instances,  directly  into  the  equatorial 
regions.  But,  in  consequence  of  diurnal  rotation,  the  air,  when 
it  arrives  at  the  equator,  is  in  a  region  which  is  moving  toward 
the  east  120  miles  an  hour  faster  than  in  latitude  30°,  where  it 
began  to  blow  as  trade  winds.  In  thus  passing  from  regions  of 
lesser  velocity  to  a  region  of  greater  velocity  the  trade  winds 
are  deflected  toward  the  west,  becoming  in  the  northern  hemi- 
sphere northeast  winds  and  in  the  southern,  southeast  winds. 

Variable  Winds.  —  North  and  south  of  the  trades  are  the 
zones  of  the  so-called  variable  winds.  They  extend  from  the 
parallels  of  30°  north  and  south,  to  the  polar  circles.  Within 
these  limits  the  prevailing  direction  of  the  winds  is  counter  or 
oppo.site  to  that  of  the  trades;  that  is,  from  the  southwest  in 
the  northern,  and  from  the  northwest  in  the  southern  hemisphere. 
For  this  reason  these  winds  are  called  coiDiter  trades.  They 
are  also  known  as  anti-trades  and  prevailing  tvesterlies. 

Their  origin  is  thus  explained  :  While  the  trades  blow  stead- 
ily from  the  poles,  there  must  be  return  currents  from  the 
equator  to  the  poles,  otherwise  the  polar  regions  in  time  would 


222  ATMOSPHERIC   CIRCULATION 

be  destitute  of  air.  When  the  upward  current  at  the  equator 
has  risen  to  a  considerable  elevation  it  divides  and  flows  toward 
the  poles,  one  part  going  toward  the  north,  and  the  other 
toward  the  south  pole. 

These  two  streams  of  air  remain  upper  currents  as  far  as 
the  northern  and  the  southern  limits  of  the  trade  winds; 
that  is,  about  as  far  as  the  parallels  of  30°  north  and  south. 

Here,  for  the  reason  that  their  temperature  has  fallen  below 
that  of  the  air  inflowing  from  the  poles,  they  descend  and  blow 
as  surface  winds.  They  become  variable,  since  they  are  fre- 
quently interrupted  by  great  swirls  or  cyclonic  movements 
following  in  the  same  general  course ;  that  is,  from  the  south- 
west to  the  northeast. 

That  the  upper  currents  above  alluded  to  do  flow  out  northward  and 
southward  from  the  equatorial  regions  is  abundantly  proved.  Sometimes 
volcanoes,  as  we  have  already  learned,  eject  vast  quantities  of  dust.  Not 
unfrequently  this  passes  into  very  elevated  regions  of  the  atmosphere ;  and 
instances  are  on  record  of  its  being  carried  sometimes  for  hundreds  of  miles 
in  a  direction  opposite  to  that  of  the  surface  winds. 

Conseguina,  in  Nicaragua,  is  in  the  region  of  the  northeast  trades.  Dur- 
ing the  eruption  of  1835,  its  ashes  were  carried  to  the  island  of  Jamaica, 
distant  800  miles  to  the  northeast.  No  other  explanation  of  this  seems 
possible,  than  that  an  upper  current  was  blowing  above  the  surface  winds, 
in  an  opposite  direction. 

In  18 1 5,  ashes  from  a  volcano  in  the  island  of  Sumbawa,  near  Java,  were 
borne  to  the  island  of  Amboina,  800  miles  to  the  northeast,  although  the 
southeast  monsoon  was  then  at  its  height.  This  again  proves  that  there  must 
have  been  a  powerful  current  toward  the  northeast,  above  the  southeast 
surface  wind.  It  is  clear,  therefore,  that  return  currents  flow  from  the 
equator  to  the  poles. 

Were  it  not  for  the  earth's  rotation,  the  counter  trades  would 
move  straight  to  the  poles.  They  are,  however,  influenced  by 
that  force  and  so  deflected  as  to  blow  from  the  southwest  or 
west.  This  is  explained  as  follows:  In  the  equatorial  regions, 
these  winds  have  acquired  the  rapid  rotary  motion  toward  the 
east  which  belongs  to  that  portion  of  the  earth.  Hence,  when 
they  reach  the  latitudes  nearer  the  poles,  they  are  blowing  east- 


THE   CALM    BELTS  223 

ward  with  a  velocity  far  more  rapid  than  that  belonging  to  those 
regions,  and  thus  become  westerly  or  southwesterly  winds. 

The  polar  winds  are  currents  of  cold  air  making  their  way 
from  the  poles  toward  the  equator.  Their  direction  is  similar 
to  that  of  the  trade  winds,  northeast  in  the  northern  hemi- 
sphere, and  southeast  in  the  southern  hemisphere.  Coming 
from  the  equator,  the  counter  trades  bring  moisture  and 
warmth  ;  the  polar  winds  are  dry  and  cold. 

The  trades,  counter  trades,  and  polar  winds,  though  treated 
separately,  are  really  only  parts  of  a  great  atmospheric  move- 
ment which  is  ceaselessly  accomplishing  its  unending  circuit 
from  the  equator  to  the  poles,  and  from  the  poles  back  to  the 
equator. 

The  Calm  Belts.  —  Between  the  northeast  and  the  southeast 
trade  winds  there  is  a  belt  of  calms  encircling  the  earth  known 
as  the  Equatorial  Calm  Belt.  The  name  is  not  altogether  good, 
for  throughout  the  entire  region  a  vast  current  of  air  is  ascend- 
ing. It  is  therefore  an  area  of  low  barometric  pressure,  and 
is  calm  only  in  the  sense  of  being  comparatively  free  from 
the  horizontal  movements  of  the  atmosphere  or  those  that  are 
ordinarily  recognized. 

The  portion  of  this  belt  resting  upon  the  sea  is  the  most 
difficult  part  of  the  ocean  for  sailing  vessels  to  cross.  By 
sailors  it  is  called  the  doldrums.  Ships  are  sometimes  detained 
here  many  days. 

Between  the  trades  and  counter  trades,  in  each  hemisphere, 
there  are  also  belts  of  atmosphere  marked  by  the  prevalence  of 
calms.  The  belt  in  the  northern  hemisphere  is  known  as  the 
Calms  of  Cancer ;  that  of  the  southern,  as  the  Calms  of  Capricorn. 
These  calms,  where  they  occur  on  the  ocean,  are  termed  by  sea- 
faring men  horse  latitudes.  Here,  unlike  the  Equatorial  Calm 
Belt,  the  air  currents  are  descending  and  the  area  is  one  of 
high  barometer. 

The  position  of  all  the  calm  and  wind  belts  above  described 
is  not  invariably  fixed.  They  all  move  northward  and  south- 
ward, following  the  apparent  course  of  the  sun.     They  reach 


224  ATMOSPHERIC   CIRCULATION 

their  farthest  northward  limit  in  autumn,  their  farthest  southern 
limit  in  spring. 

The  Periodical  Winds  are  those  which  blow  for  a  certain  time 
in  one  direction,  and  then  for  an  equal  or  nearly  equal  time,  in 
the  opposite  direction.  They  are  the  land  and  sea  breezes  and 
the  mojisoons. 

Along  the  coast  of  most  countries  there  is  a  breeze  from  the 
sea  by  day  and  from  the  land  by  night.  The  rays  of  the  sun 
heat  the  land  more  readily  than  they  do  the  water.  The  warm 
rocks,  sand,  and  soil  heat  and  expand  the  air  in  contact  with 
them,  rendering  it  light.  Pressed  upward  by  the  cooler  air^of 
the  sea,  it  rises.  Currents  then  rush  from  off  the  sea  to  supply 
the  place  of  the  ascending  columns,  precisely  as  the  indraught 
to  a  furnace  supplies  the  rush  up  the  chimney.  Thus  a  sea 
breeze  is  produced. 

At  night  this  action  is  reversed.  The  land  has  the  property 
of  radiating,  that  is,  of  parting  with,  its  heat  more  rapidly  than 
the  water,  hence  the  land  by  night  grows  cooler  than  the  sea. 
It  then  cools  the  air  above  it.  But  the  air  over  the  sea  remains 
comparatively  warm  and  light  and  is  therefore  pressed  upward 
by  the  cool  air  from  the  land  in  the  form  of  seaward-blowing 
currents.     They  constitute  the  land  breeze. 

Were  it  not  for  these  refreshing  breezes,  many  countries  along 
the  seacoast  would  be  uninhabitable. 

/  Monsoons  are  winds  which  blow  from  a  certain  direction 
for  part  of  the  year,  and  for  the  rest  of  the  year  from  quite  an- 
other quarter.  They  are  land  and  sea  breezes  on  a  grand  scale. 
Instead  of  alternating  with  day  and  night,  they  alternate  with 
summer  and  winter,  hence  their  name,  from  an  Arabic  word 
meaning  season. 

The  most  famous  monsoons  are  those  of  southern  Asia.  In 
India  they  blow  from  the  northeast  for  six  months  of  the  year, 
and  from  the  southwest  for  six  months. 

During  the  summer  the  sun  plays  upon  the  great  deserts  and 
inland  basins  of  central  Asia.  Those  dry  and  barren  wastes 
glow  like    furnaces,  and  the  heated  air  ascends  from  them  in 


THE   PERIODICAL    WINDS  225 

immense  columns.  A  disturbance  is  created  which  is  felt  to 
the  distance  of  2000  or  3000  miles  from  its  center.  Cooler  air 
rushes  in  from  the  sea  on  three  sides  of  the  continent.  Along 
the  coasts  of  Siberia  it  comes  from  the  north.  P^rom  China 
round  the  south  of  the  continent  to  the  Red  Sea,  it  comes  from 
the  Pacific  and  Indian  oceans  ;  that  is,  from  the  southeast, 
south,  or  southwest. 

In  this  region,  which  is  largely  in  the  zone  of  "  trades,"  the 
effect  is  so  great  as  actually  to  reverse  the  trade  wind  and  cause 
it  to  blow  in  the  contrary  direction. 

In  the  winter  the  center  of  Asia  is  a  region  of  low  tempera- 
ture. Its  atmosphere  is  dry,  cold,  and  heavy ;  that  of  the 
seas  south  and  east  of  the  continent  is  moist,  warm,  and  light. 
The  light  air  is  pressed  upward  by  the  heavy,  and  ascends 
into  the  upppr  regions  of  the  atmosphere.  Currents  then  blow 
from  the  land  toward  the  sea.  In  consequence  of  this  we 
have,  during  the  winter  in  India,  ?he  northeast  monsoons, 
which  are  really  the  northeast  trades  blowing' with  augmented 
force  and  velocity  ;  on  the  Chinese  coast  we  have  the  northwest 
monsoons. 

The  summer  or  the  southeast  and  southwest  monsoons,  hav- 
ing passed  over  the  sea,  are  laden  with  moisture,  and  are  the 
wet  monsoonsj^  They  give  its  wet  season  to  southern  Asia. 
The  northeast  and  northwest  monsoons  are  for  the  most  part  dry, 
because  they  come  from  the  land.  During  their  prevalence  it  is 
the  dry  season.  The  changing  from  the  dry  winds  to  the  wet 
is  called  in  India  the  "bursting  "  of  the  monsoon. 

The  southwest  monsoon  sets  in  generally  toward  the  end  of  April,  a  steady 
wind  sweeping  up  from  the  Indian  Ocean  and  carrying  with  it  dense  volumes 
of  vapor.  The  atmosphere  becomes  close  and  oppressive.  Flashes  of  light- 
ning play  from  cloud  to  cloud.  The  wind  suddenly  springs  up  into  a  tempest. 
Then  a  few  great  heavy  drops  of  rain  fall ;  the  forked  lightning  is  changed  to 
sheets  of  light,  and  suddenly  the  flood  gates  of  heaven  are  opened,  and  not 
rain,  but  sheets  of  water,  are  poured  forth,  refreshing  the  parched  earth,  carry- 
ing fertility  over  the  surface  of  the  country,  filling  the  wells  and  reservoirs,  and 
replenishing  the  dwindling  rivers  and  streams.  The  whole  land  from  Cape 
Comorin  to  Bombay  seems  suddenly  recalled  to  life. 


226  •  ATMOSPHERIC   CIRCULATION 

Certain  other  winds  resembling  the  monsoons  are  those  of 
Australia,  the  Gulf  of  Guinea,  and  the  Mediterranean.  They 
are  sometimes  called  minor  monsoons. 

The  winds  of  Australia  blow  landward  in  the  hot  months  ;  seaward  in  the 
cold  season.  They  are  largely  controlled  by  the  great  desert  of  Australia  at 
the  one  season  and  by  that  of  Gobi  at  the  other.  During  the  South  Temper- 
ate summer  the  Australian  desert  is  the  hotter.  During  the  South  Temperate 
winter  Gobi  is  the  hotter.     Each  thus  becomes  in  turn  the  controlling  area. 

The  Australian  monsoons,  however,  do  not  compare  in  regularity  with  those 
of  India. 

Over  the  Gulf  of  Guinea  and  the  Mediterranean  periodical  winds  blow  in 
summer  in  opposite  directions  ;  the  winds  of  the  Gulf  of  Guinea  come  from  the 
southwest,  those  of  the  Mediterranean  —  known  to  the  ancient  Greeks  as  the 
Etesian  winds  —  are  from  the  northeast.  Both  are  due  to  one  cause,  namely, 
the  intense  heating  of  the  Sahara.  This  produces  an  upward  current  of  heated 
air  and  an  inrush  of  cooler  air  from  the  Gulf  of  Guinea  on  the  one  side,  and 
from  the  Mediterranean  on  the  other. 

The  periodical  winds  of  Mexico,  Central  America,  and  the  Brazilian  waters, 
and  those  known  in  Texas  as  "  Northers,"  are  due  to  causes  similar  to  those 
of  the  monsoons. 

Among  the  periodic  winds  of  less  importance  are  the  return 
currents  from  deserts.  These  are  laden  with  heat,  sand,  and 
dust. 

From  the  Sahara  currents  flow  northward  and  southward.  Those  from 
the  south  enter  Egypt,  and  blow  for  a  few  days  at  a  time  during  a  period  of 
50  days.  Hence  they  are  called  khamsin,  an  Arabic  word  meaning  fifty. 
During  their  prevalence  the  air  is  filled  with  blinding  dust  and  the  midday  sun 
is  darkened.  By  such  a  wind  of  unusual  violence,  the  army  of  Cambyses, 
50,000  in  number,  is  said  to  have  been  destroyed,  when  on  its  way  to  attack 
the  oasis  and  temple  of  Jupiter  Ammon. 

Crossing  the  Mediterranean,  the  desert  wind  scorches  the  vegetation  of 
southern  Europe.     It  is  known  as  the  sirocco. 

The  tops  of  mountains  chill  the  surrounding  air.  This  some- 
times descends  as  a  cold  wind  into  the  warmer  regions  below. 
Thus  from  the  snowy  heights  of  the  Andes  the  cold  pamperos 
sweep  over  the  Pampas  of  the  Plata,  the  icy  puna  descends 
upon  the  table-land  of  Peru,  and  the  chilling  Diistral  descends 
from  the  Alps  to  the  shores  of  the  Mediterranean,  causing  great 
discomfort  to  sick  and  well. 


SURFACE  EFFECTS  OF  WINDS 


■^-V 


Surface  Effects  of 
Winds  are  especially 
well  shown  along 
sandy  coasts  and  in 
arid  regions.  By  the 
constant  blowing  of 
the  wind  sand  is  ac- 
cumulated in  rounded 
ridges,  like  snowdrifts, 
called  dunes.  These 
heaps  are  by  no  means 
stationary,  but  advance 
with  the  wind,  some- 
times     overwhelming 


Sand  Ijlm 


Showing  the  general    level    surface   and   the   steep   lee 
slope  encroaching  on  a  pine  forest.  * 


forests  and  converting  arable  lands  into  barren  wastes.     Large 
dunes  are  found  on  the  southwest  coast  of  France.     Here  for 


r^--?^--;;^- 

^.'^i 


_5r« 


Surface  of  Dune,  Dune  Park,  iNniANy? 
Showing  the  destruction  of  a  forest  by  dune  invasion.     (From  United  States  Geological 

Survey.) 


228  ATMOSPHERIC   CIRCULATION 

the  distance  of  150  miles  they  cover  a  strip  several  miles  wide, 
attaining  in  some  instances  the  height  of  300  feet.  At  the  head 
of  Lake  Michigan  and  on  its  eastern  shore  are  found  large 
dunes.  On  the  Pacific  coast,  near  the  Golden  Gate  and  else- 
where, the  drifting  of  the  sand  has  been  prevented  by  the  culti- 
vation of  certain  plants.  The  heaping  up  of  sand  ridges  in 
desert  regions  through  wind  action  is  also  common,  as  in  Africa, 
Arabia,  and  the  Great  Basin.  Moreover,  blowing  sand  is  an 
agent  of  abrasion  and  by  it  even  rocks  are  worn  away. 

Among  other  surface  effects  of  wind  mention  may  be  made  of 
the  stripping  of  land  surfaces,  the  transportation  of  dust,  and  the 
destruction  of  forests. 


XXI.    STORMS 

General  Description.  —  Storms  and  tempests  are  sudden  and 
violent  disturbances  of  the  atmosphere.  At  sea  they  are  among 
the  most  grand  and  terribly  sublime  spectacles  in  nature.  A 
wind  becomes  a  storm  when  it  attains  the  velocity  of  50  miles 
or  more  an  hour. 

The  great  storms  of  the  West  Indies  and  of  the  Indian  Ocean 
are  called  hurricanes  ;  those  of  the  China  Sea,  typhoons.  These 
storms,  which  are  alike  in  cause  and  character,  together  with  the 
great  eastward-moving  swirls  of  the  temperate  regions,  may  be 
considered  under  the  general  name  of  cyclone.  This  word,  de- 
rived from  the  Greek  kuklos,  circle,  refers  to  the  fact  that  they 
consist  of  columns  of  air  revolving  round  a  perpendicular  axis. 


Sketch  to  illustrate  the  Lower- atmospheric  Circulation  in  a  Hurricane 
The  inward  spiral  at  the  base  is  the  surface  wind.      (After  Everett  Hayden  in  National 
Geographical  Magazine^ 

At  the  same  time  they  have  a  progressive  motion  of  greater  or 
less  rapidity  over  a  certain  portion  of  the  surface  of  the  earth. 

Cause  of  Storms. — The  general  cause  of  all  such  atmospheric 
disturbances  is  the  same  in  principle  as  that  of  ordinary  winds. 

229 


230 


STORMS 


COURSEOF  CYCLONE 

IN 
Northern  Hemisphere 


^a^e 


COURSEOF  CYCLONE 

IN 

Southern  Hemisphere 


Course  of  Cyclones 


It  is  a  difference  or  inequality  of  pressure  or  weight,  in  different 
regions  of  the  atmosphere.  The  principle  may  be  thus  stated  : 
Into  an  area  of  low  barometer  a  wind  must  always  blow  from  an 
area  of  high  barometer. 

When  from  any  cause  the  weight  of  the  atmosphere  in  a  locality 

is  diminished,  an 
ascending  current 
results.  Currents 
of  colder  and 
heavier  air  rush 
in  to  supply  the 
deficiency.  The 
force  and  velocity 
of  the  currents 
thus  created  will  be 
greater  or  less  ac- 
cording to  the  dif- 
ference of  atmos- 
pheric pressure, 
or  the  "gradient," 
as  meteorologists 
call  this  differ- 
ence. The  larger 
the  gradient,  the 
more  violent  will 
be  the  resulting 
wind. 

Suppose  there 
is  but  one  area  of 
low  barometer  and 
one  of  high  ;  the 
result  will  be  a 
simple  wind  moving  in  one  direction.  If,  however,  the  one 
area  of  low  barometer  is  surrounded  by  areas  of  high  barometer, 
it  is  evident  that  there  will  be  an  inflow  of  air  from  all  directions. 
Such  currents  do  not  collide  at  the  center,  but,  in  obedience  to 


LAWS  OF  STORMS 


231 


a  force  arising  from  the 
earth's  rotation,  are  de- 
flected to  the  right  in 
the  northern  hemisphere 
and  to  the  left  in  the 
southern.^  They  there- 
fore circle  round  this 
area,  thus  forming  a  cy- 
clone. The  course  of 
the  atmospheric  currents 
during  a  disturbance  of 
this  kind  is  shown  in  the 
diagram  on  p.  229. 

Laws  of  Storms.  — 
Cyclones  obey  the  fol- 
lowing laws:  — 

( I )  The  wind  revolves 
in  opposite  directions 
according  as  the  cyclone 
is  in  the  northern  or 
southern  hemisphere.;  In 
the  northern  the  direc- 
tion of  revolution  is  from 
right  to  left,  or  against 
the  hands  of  a  watch. 
In  the  southern  it  is 
from  left  to  right,  or  with 
the  hands  of  a  watch. 

As  the  wind  constantly  re- 
volves, it  constantly  changes 
its  direction  at  any  given  place 
in  the  storm  track.  On  oppo- 
site sides  of  the  center  it  has 
opposite  directions.  Hence 
it  is  easy  to  understand  why 


NORTHERN  HEMISPHERE 

VVindEast 


SOUTHERN  HEMISPHERE 

VJind  West 


Wind  East 

Storm  Cards 

Showing  direction  of  whirl  in  both  hemispheres. 

^  Ferrel's  law. 


M.-S.  PHYS.  GEOG. 


14 


232  STORMS 

the  wind  changes  as  soon  as  the  storm  center  passes.     This  is  shown  by  the 
"  storm  cards." 

The  rate  of  revolution,  or  "velocity  of  the  wind,"  is  from  50  to  150  miles 
an  hour. 

(2)  The  storm,  while  revolving,  has  a  progressive  motion. 
The  direction  of  this  motion  is  determined  by  the  prevailing 
winds.  In  general  it  is  northwest  and  southwest  within  the 
zones  of  the  trades,  and  northeast  and  southeast/in  those  of  the 
counter  trades.  / 

The  course  of  tropical  cyclones  is  well  defined.  North  of  the 
equator  they  move  northwestwardly  up  to  about  latitude  30°  N. 
Here  they  turn  to  the  northeast.  South  of  the  equator  they 
pursue  the  reverse  course ;  starting  near  the  tropics,  they  advance 
toward  the  southwest,  and  near  the  parallel  or  27°  they  turn  to 
the  southeast.  From  this  it  will  be  seen  that  the  pathway  of 
cyclones  somewhat  resembles  the  curve  called  a./)  a  ra  do /a.  (See 
diagram,  p.  230.)  The  rate  of  travel  varies  from  i  to  70  miles 
an  hour. 

(3)  The  storm  center  is  an  area  of  calm  and  also  of  low 
barometer.  The  arrival  of  the  storm  center  at  any  point  is 
indicated  by  the  barometer.  The  descent  of  the  mercury  in 
tropical  storms  often  amounts  to  two  inches.  It  is  sometimes 
so  rapid  that  it  can  be  detected  by  the  eye. 

This  fall  of  the  barometer  occurs  at  the  storm  center  for  two 
reasons  :  ist,  because  the  center  is  an  area  of  warm,  humid  air; 
2d,  because  the  center  is  an  area  of  rarefaction. 

The  air  particles  which  are  nearest  the  vertical  center  of  the  cyclone  are 
apparently  repelled  outward  from  that  center  by  their  centrifugal  force. 
This  makes  the  air  in  the  center  less  dense,  or,  as  we  commonly  say,  rare- 
fies  it.  Under  such  conditions  the  barometric  column  sometimes  falls  as  low 
as  27.5  inches. 

Anti-cyclones.  —  Closely  associated  with  cyclones  are  vast 
bodies  of  air  the  condition  of  which  is  the  reverse  of  that  of  the 
cyclone.  To  such  bodies  of  air  is  given  the  name  anti-cyclone; 
that  is,  opposite  of  the  cyclone. 

The  cyclone  is  warm,  moist,  and  light.     The  anti-cyclone  is 


VALUE   OF   STORM    LAWS  233 

cold,  dry,  and  heavy.  Hence  the  area  over  which  an  anti- 
cyclone prevails  is  one  of  high  barometer.  Occasionally  in  an 
anti-cyclone  the  mercury  will  rise  to  31.25  inches. 

Again,  while  in  a  cyclone  air  currents  flow  inward  from  the 
circumference  toward  the  center,  in  the  anti-cyclone  currents 
flow  outward  from  the  center  toward  the  circumference. 

Value  of  Storm  Laws. — A  knowledge  of  the  laws  of  storms 
is  of  the  utmost  value  to  the  navigator.  By  observing  the 
direction  of  the  wind  he  may  learn  in  what  direction  the  storm 
center  is  from  him.  The  rule  is  :  Turn  your  back  to  the  wind 
and  the  low  barometer  is  always  to  your  left  in  the  northern 
hemisphere,  and  in  the  southern  hemisphere  to  your  right.  This 
will  appear  by  examining  the  diagram  on  page  231,  and  imagin- 
ing yourself  with  your  back  to  the  arrowheads.  If  the  sailor 
knows  where  the  storm  center  is,  he  can  steer  away  from  it. 

Again,  if  he  finds  his  barometer  sinking  rapidly,  an  inch  or 
more  below  its  usual  height,  he  knows  that  he  is  in  the  storm 
center.  Obviously  it  will  be  well  to  trim  the  sails  and  prepare 
for  a  gale.  The  center  of  calm  will  soon  pass  beyond  and  a 
tempest  strike  his  ship. 

The  Areas  of  Storms  differ  in  size  and  shape.  In  Europe 
they  are  nearly  circular  ;  in  the  United  St-ates,  their  shape  is 
usually  an  elongated  oval.  They  are  seldom  less  than  600 
miles  in  diameter.     They  average  twice  that  amount. 

Tornadoes  and  Whirlwinds  differ  from  hurricanes  and  ty- 
phoons, (i)  in  duration  ;  and  (2)  in  extent  of  area. 

In  passing  over  any  point,  tornadoes  seldom  occupy  more 
than  a  few  seconds.  Their  breadth  varies  from  a  few  yards  to 
a  mile  or  two,  though  their  destructive  effects  are  usually  con- 
fined to  a  narrow  path. 

The  rate  of  their  progressive  motion  is  commonly  about  30 
miles  an  hour,  and  the  length  of  the'ir  course  25  or  30  miles. 

An  approaching  tornado  has  the  form  of  a  funnel-shaped 
cloud  pointing  downward.  A  noise,  perhaps  due  to  electricity, 
and  not  unlike  that  of  a  train  of  cars,  is  heard  ;  thunder,  light- 
ning, hail,  and  rain  occur. 


234 


STORMS 


A  partial  vacuum  is  formed  by  the  centrifugal  force  at  the 
center.     Sometimes  when  the  end  of  the  funnel  dips  down  and 
touches  a  building,  the  vacuum  resting  over  it  so  relieves  the 
building  from  atmospheric  pressure  as  to  cause  a  sudden  expan- 
sion of   the  air  con- 
tained in  it.  The  walls 
of  the  building  then 
burst  asunder  as  by 
explosive  force. 

Tornadoes  sweep 
everything  before 
them.  Houses  and 
other  buildings  are 
lifted  up  bodily,  and 
lanes  called  "  wind 
roads  "  are  cut 
through  the  forests. 
Large  trees  are  up- 
rooted and  whirled 
about  like  stubble. 

The  region  of 
North  America  most 
frequently  visited  by 
tornadoes  is  the  Mis- 
sissippi Valley.  Dur- 
ing the  past  50  years 
more  than  600  have 
occurred  there. 

In  the  deserts  of 
Asia  and  Africa,  as 
well  as  in  the  region 
of  the  Great  Basin  of  North  America,  whirlwinds  sometimes 
draw  up  into  their  central  core  large  quantities  of  sand  and  dust. 
They  thus  become  moving  columns  of  sand,  500  to  700  feet  in 
height  (as  observed  with  sextant),  and  are  known  as  "  dust 
whirlwinds," 


^■■i^^l 

QUI 

5P"r'      •■*  •'♦*' 

A    lOKNADO 

The  tornado  here  shown  is  from  a  photograph  taken  by 
Mr.  W.  E.  Seright  at  Stafford,  Kansas,  about  5 :  30 
P.M.,  April  12,  1906.  It  was  the  last  of  six  or  seven 
similar  manifestations  which  occurred  within  the 
radius  of  three  or  four  miles  the  same  afternoon. 
When  photographed  the  cloud  was  probably  a  mile 
distant  in  a  northeast  direction. 


J 


DISTRIBUTION   OF   STORMS 


235 


The  Simoom,  or  "  poison  wind,"  appears  to  be  a  desert  whirl- 
wind intensely  hot,  and  so  rarefied  as  to  be  suffocating. 

At  sea,  especially  in  cer- 
tain parts  of  the  ocean, 
waterspouts  occur.  These 
are  tall  moving  columns 
of  water.  Scientific  opinion 
is  divided  as  to  their  cause. 
Some  think  that  they  are 
produced  like  the  dust 
whirlwinds  of  the  desert, 
by  a  revolving  air  current 
which  draws  up  the  spray 
of  the  waves  into  its  core 
of  low  pressure.  Others 
think  that  the  water  comes 
solely  from  the  clouds. 
The  cut  seems  to  suggest 
the  latter  view.  Two 
actual,  careful  observers  of 
the  spout  photographed 
drew,  however,  opposite 
conclusions  from  their 
observations. 

Distribution  of  Storms. — 
The  most  violent  storms 
occur  in  the  vicinity  of 
mountainous  islands. 

The  Pacific  is  the  most 
tranquil  of  the  oceans.     In 
those  portions  of  its  trade-     Waterspout   as  seen    ekom    Oak    Bluffs 
^  (Cottage  City),  Mass.,  August  19,  1896, 

wind  regions  where  there  at  1:02  p.m. 

are  no  islands,  and  where 

monsoons  do  not  prevail,  storms  are  almost  unknown.  The 
typhoons  are  confined  to  the  southeast  coasts  of  Asia  and  the 
East  India  Archipelago. 


236 


WEATHER    FORECASTS  237 

The  South  Atlantic,  along  the  coast  of  intertropical  Brazil, 
is  almost  stormless,  whereas,  in  corresponding  latitudes  in  the 
North  Atlantic,  among  the  West  Indies,  terrific  hurricanes 
occur. 

The  portions  of  the  Indian  Ocean  especially  subject  to 
hurricanes  are  the  Bay  of  Bengal  and  the  neighborhood  of 
Mauritius. 

Weather  Forecasts,^  —  During  the  last  50  years  observa- 
tions upon  the  force  and  direction  of  the  wind,  the  course 
and  character  of  storms,  the  pressure  of  the  atmosphere,  the 
amount  of  rainfall,  the  temperature  and  moisture  of  the  air, 
have  disclosed  certain  general  principles  or  laws  of  the  weather. 

Knowing  these  laws,  and  knowing  by  telegraphic  reports 
the  weather  conditions  prevailing  throughout  the  country,  it 
is  possible  to  predict  from  day  to  day,  with  considerable  accu- 
racy, the  approach  of  storms,  or  of  cold  or  hot  weather. 

Most  of  the  great  storms  of  the  United  States  travel  in  a 
northeasterly  direction.  They  may  be  conveniently  classed  as 
those  which  come  from  the  Pacific  Ocean  and  those  which 
come  from  the  Atlantic. 

The  storms  of  the  Pacific  penetrate  to  a  greater  or  less  dis- 
tance into  the  country,  and  often  cross  it  entirely. 

The  storms  from  the  Atlantic  are  first  felt  either  at  some 
southerly  point  on  the  Atlantic  seaboard,  or  on  the  shores  of 
the  Gulf.  Generally  they  come  in  from  sea  by  the  way  of  the 
Gulf,  pass  northward  through  the  Mississippi  Valley,  and  then 
turn  to  the  northeast. 

J  Over  50  years  ago  Maury  urged  upon  the  attention  of  the  government  of  the 
United  States,  and  those  of  European  nations,  the  desirability  of  having  systematic 
meteorological  observations  carried  on  by  all  nations  at  sea.  As  the  result  of  his 
efforts  the  United  States  government  invited  all  the  maritime  states  of  Christendom 
to  a  conference,  which  took  place  in  Brussels,  1853.  The  suggestions  made  were 
adopted.  But  the  ideas  of  Maury  were  not  limited  to  the  ocean.  In  the  preface  to 
the  second  edition  of  his  "Physical  Geography  of  the  Sea,"  published  in  1855,  he 
says  :  "It  is  a  pity  that  the  system  of  observations  recommended  by  the  conference 
should  relate  only  to  the  sea.  The  plan  should  include  the  land  also,  and  be  uni- 
versal." The  present  "  U.  S.  Weather  Bureau "  with  its  well-organized  Signal 
Service  is  the  crowning  result  of  his  labors  in  this  direction. 


238  STORMS 

Those  which  make  their  appearance  first  on  the  Atlantic  seaboard  are  the 
western  halves  of  cyclones,  which,  pursuing  their  parabolic  course,  first  north- 
westwardly and  then  northeastwardly,  happen  partially  to  embrace  our  shores 
within  their  area.  These  western  half-cyclones  consist  of  northeast  and 
northwest  gales.  The  eastern  halves  of  the  same  storms,  consisting  of  gales 
from  the  southwest  and  southeast,  are  at  sea.  The  storm  center  pursues  a 
course  nearly  coinciding  with  our  shore  line. 

The  transient  and  uncertain  character  of  tornadoes  renders  it 
impossible  to  make  exact  predictions  regarding  them. 

Ordinary  storms,  however,  are  so  far  regular  that,  in  a  large 
proportion  of  cases,  their  course,  after  they  have  once  manifested 
themselves,  may  be  foretold  with  some  degree  of  accuracy. 

The  Weather  Map.  —  The  following  description  of  the 
Weather  Map  is  taken  from  a  publication  by  the  Chief  of 
the  United  States  Weather  Bureau  (see  map,  p.  236):  "This 
map  presents  an  outline  of  the  United  States  and  Canada,  and 
shows  stations  where  weather  observations  are  taken  daily  at 
8  A.M.  and  8  p.m.,  seventy-fifth  meridian  time.  These  obser- 
vations consist  of  readings  of  the  barometer,  thermometer  (dry 
and  wet),  direction  and  velocity  of  the  wind,  state  of  weather, 
amount,  kind,  and  direction  of  the  clouds,  and  amount  of  rain 
or  snow,  and  are  telegraphed  to  Washington  and  to  many  of 
the  Weather  Bureau  stations  throughout  the  country  for  publi- 
cation on  maps  and  bulletins.  Solid  lines,  called  isobars,  are 
drawn  through  points  having  the  same  atmospheric  pressure ; 
a  separate  line  being  drawn  for  each  one  tenth  of  an  inch  in 
the  height  of  the  barometer.  Dotted  lines,  called  isotJierms, 
connecting  places  having  the  same  temperature,  are  drawn  for 
each  10  degrees  of  the  thermometer.  Heavy  dotted  lines, 
inclosing  areas  where  a  decided  change  of  temperature  has 
occurred  within  the  last  24  hours,  are  sometimes  added.  The 
direction  of  the  wind  is  indicated  by  an  arrow  flying  with 
the  wind,  or  opposite  to  the  ordinary  vane.  The  state  of 
the  weather  —  whether  clear,  partly  cloudy,  cloudy,  raining,  or 
snowing  —  is  indicated  by  the  circular  symbol.  Shaded  areas, 
when  used,  show  where  rain  or  snow  has  fallen  since  the  last 
observation." 


J 


XXII.     MOISTURE   OF   THE    AIR 

Humidity.  —  More  or  less  moisture  is  always  present  in  the 
air.  It  exists  as  vapor.  This  vapor  is  invisible,  yet  its  presence 
is  often  recognized  by  the  sensation  of  dampness.  The  amount 
of  vapor  in  the  air  is  greater  over  the  sea  and  other  large  bodies 
of  water  than  over  the  land.  It  is  dissipated  by  heat  and  con- 
densed by  cold.  In  arid  regions  the  moisture  available  is  less 
than  the  capacity  of  the  air  to  hold,  hence  the  air  is  dry.  The 
presence  or  absence  of  moisture  in  the  atmosphere  has  a  marked 
effect  on  climate.  Great  humidity  is  enervating  and  not  con- 
ducive to  mental  or  physical  exertion ;  temperature  sensations 
are  exaggerated  ;  human  activities  curtailed.  Dry  air,  on  the 
contrary,  is  bracing,  and  higher  temperatures  can  be  endured 
without  discomfort. 

Evaporation. —  One  of  the  most  remarkable  properties  of  water 
is  the  readiness  with  which  it  passes  from  one  of  its  states  to 
another.  Whenever  it  assumes  the  form  of  vapor  it  is  said  to 
evaporate,  and  the  process  of  evaporation  goes  on  at  all  tempera- 
tures and  under  all  circumstances  until  the  air  is  saturated. 
When  the  point  of  saturation  has  been  reached,  it  can  hold  no 
more  moisture. 

You  may  have  observed  water  drying  in  the  streets  and  roads  after  a  rain, 
or  clothes  hanging  on  the  line  frozen  stiff,  and  yet  becoming  dry  ;  or  you  may 
have  seen  a  light  fall  of  snow  disappear  in  freezing  weather.  These  were  cases 
of  evaporation. 

Evaporation  is  accelerated  and  increased  under  the  following 
conditions  :  — 

(i)  By  high  temperature.  From  this  it  follows  that  the  maxi- 
mum of  evaporation  is  found  within  the  tropics ;  the  minimum 
at  the  poles.  Furthermore,  that  evaporation  takes  place  during 
the  day,  and  in  the  warmest  part  of  the  day 

239 


240  MOISTURE   OF  THE   AIR 

(2)  By  diminution  of  pressure.  In  a  vacuum  there  is  almost 
no  pressure,  and  there  evaporation  takes  place  almost  instan- 
taneously. Hence  on  the  tops  of  high  mountains,  where  the 
pressure  of  the  atmosphere  is  very  much  diminished,  evaporation 
goes  on  much  more  rapidly  than  it  does  at  the  sea  level,  where 
the  full  pressure  of  the  entire  atmosphere  is  felt. 

Indeed,  mountain  peaks  may  be  so  high  as  to  be  entirely  free 
from  snow,  while  a  belt  of  snow  girdles  the  lower  part  of  the 
mountain.  The  reason  of  this  appears  to  be  that  at  certain  alti- 
tudes and  under  certain  conditions  snow  evaporates  so  rapidly 
that  it  cannot  accumulate. 

Aconcagua  in  Chile  sometimes  appears  with  its  bare  and  bleak 
top  peering  above  a  girdle  of  snow. 

(3)  By  a  dry  condition  of  the  atmosphere.  Warm  dry  air  will 
absorb  far  more  moisture  than  that  which  is  cool  and  damp. 
If  air  be  near  the  point  of  saturation,  it  is  clear  that  evaporation 
will  be  retarded  ;    but  if  the  air  be  dry,  it  will  be  accelerated. 

(4)  By  wind.  If  a  wind  blows  upon  the  surface  of  water, 
evaporation  is  accelerated.  As  fast  as  one  portion  of  the  air  be- 
comes charged  with  vapor,  it  is  removed,  and  a  fresh  portion 
takes  its  place. 

Condensation  and  Precipitation. — Vapor  returns  to  the 
liquid  or  solid  state  and  is  deposited  upon  the  earth  by  the  pro- 
cesses called  condensation  and  precipitation. 

When  condensed,  it  assumes  the  form  of  dew,  white  or  hoar- 
frost, fog  or  cloud,  hail  or  snow. 

The  great  cause  of  precipitation,  or  the  removal  of  moisture 
from  the  atmosphere,  is  loss  of  heat.  The  atmosphere  can 
contain  more  or  less  vapor  in  a  state  of  absorption  in  proportion 
to  its  temperature.  If  the  temperature  is  50°,  a  cubic  foot  of  air 
can  absorb  about  two  grains'  weight  of  vapor.  At  the  tempera- 
ture of  70°,  that  is,  with  an  increase  of  only  20°  of  heat,  the 
proportion  of  vapor  is  about  twice  as  great. 

From  this  it  is  easy  to  see  why  reduction  of  temperature  causes 
precipitation.  Suppose  a  cubic  foot  of  air  saturated  with  mois- 
ture to  be  reduced  in  temperature,  even  very  slightly ;  it  is  ob- 


HOW   DEW   IS    FORMED 


241 


vious  that  its  capacity  for  moisture  will  be  at  once  reduced, 
and  a  certain  portion  of  its  vapor  must  be  precipitated.  The 
temperature  at  which  the  deposit  in  such  cases  begins  to  take 
place  is  called  the  (/cw  point. 

How  Dew  is  Formed.  —  On  clear  and  calm  nights,  the  grass, 
the  leaves,  and  other  objects  rapidly  radiate  their  heat  and  grow 


Cirrus  Streamers  with  Low  Cumulus  on  the  Horizon,  Washington,  D.C. 
From  photograph  by  Professor  A.  J.  Henry. 

cool.  They  chill  the  surrounding  air.  It  can  no  longer  contain 
the  same  amount  of  moisture  as  when  it  was  warm.  Hence  a 
portion  of  it  is  condensed  and  deposited  upon  the  leaves  in  the 
sljape  of  fine  drops  of  water.  We  often  say  "  the  dew  begins  to 
fall,''  though,  strictly  speaking,  it  does  not  fall.  It  is  deposited 
upon  the  grass  precisely  as,  on  a  hot  summer's  day,  the  moisture 
is  deposited  on  the  outside  of  a  pitcher  of  ice  water. 

Clouds  check  radiation,  and  hence  on  cloudy  nights  less  dew, 
or  perhaps  none  at  all,  is  deposited. 

You  must  have  noticed  that  dew  and  hoar  frost,  which  is  mois- 


242 


MOISTURE   OF  THE   AIR 


ture  condensed  at  a  temperature  below  the  freezing  point,  are 
deposited  on  some  objects  more  copiously  than  others.  This  is 
because  some  radiate  heat  more  rapidly,  and  therefore  chill  and 
condense  more  quickly  the  vapor  that  floats  above  them. 

Fog.  —  Vapor  coming  in  contact  with  cool  air,  if  chilled  below 


Cirrus  Clouo  merging  into  Cirro-stkaius,  Washington,  D.C. 
From  photograph  by  Professor  A.  J.  Henry. 

the  dew-point,  assumes  the  form  of  fine  watery  particles  which 
we  call  mist  ox  fog. 

It  may  also  have  been  observed  that  in  a  clear,  calm,  and 
frosty  morning  the  springs,  ponds,  and  rivers  "  smoke."  This 
phenomenon  is  identical  with  that  exhibited  by  the  steam  which 
issues  from  the  teakettle,  the  locomotive,  and  the  steamboat. 
The  "  smoke  "  is  a  miniature  fog. 

Often,  too,  fogs  are  seen  upon  the  surface  of  rivers  in  early 
morning,  which  vanish   before   noon.     The  morning  air,  being 


CLOUDS 


243 


cool,  cannot  absorb  this  moisture,  but  later  in  the  day  when  its 
capacity  has  been  increased  by  warming,  it  readily  absorbs  the 
fog. 

The  most  foggy  sea  in  the  world  is  that  part  of  the  North  Atlantic  Ocean  that 
lies  on  the  polar  side  of  latitude  40" ;  and  the  most  foggy  place  is  on  the 
Grand  Banks  of  Newfoundland. 


DOI  KI.E-TURRETED   CUMULUS,    LOWKR    POK  I.MAC    kl\l  R 

From  photograph  by  Professor  A.  [    Henry. 

Vapor  rises  rapidly  from  the  warm  water  of  the  Gulf  Stream.  Near  the 
Grand  Banks  the  Gulf  Stream  meets  the  icy  Labrador  Current.  Owing  to  the 
chilling  influence  of  this  current,  the  vapor  is  condensed  into  fog  as  fast  as  it 
rises. 

Though  fogs  are  most  frequent  in  summer,  they  occur  on  the  Grand  Banks 
at  all  seasons,  producing  in  winter  the  exquisitely  beautiful  silver  fogs  of  New- 
foundland, which  garnish  the  forests  of  that  island  with  frostwork. 

Clouds.  —  A  cloud  is  simply  a  mass  of  mist  or  fog  floating 
high  in  the  aJr  instead  of  near  the  ground. 


244 


MOISTURE   OF  THE   AIR 


Clouds  present  a  very  great  variety  of  appearance,  and  hence 
are  divided  into  seven  classes  :  three  simple,  cirrus,  cumulus,  and 
stratus ;  four  compound,  cirro-cumulus,  cirro-stratus,  cumulo- 
stratus,  and  cunuilo-cirro-stratus  or  uimbus. 

The  cirrus  or  curl  cloud  consists  of  white  wavy  lines  or  curled 


1          " 

?E 

^^ 

\ 

wara 

g^i^ray^ 

j^^Sff^ijfe^'^" 

\              -^ 

B^^'^^ikc^^^ 

*^^^". 

\  • 

-J 

^ 

J8 

■ 

1 

iH^^gutUiimK^^ 

Cirro-cumulus  Cloud,  "Mackerel  Sky,"  Washlncjton,  D.C. 
From  photograph  by  Professor  A.  J.  Henry. 

bands.  It  is  the  lightest  of  all  cloud  forms,  and  attains  the 
highest  elevations,  floating  four  or  five  miles  above  the  surface 
of  the  earth  in  regions  of  perpetual  frost.  It  is  supposed  to 
consist  of  minute  crystals  of  ice  such  as  we  see  in  the  snowflake, 
and  may  be  defined  as  frozen  fog. 


Cirrus  clouds  are  often  heralds  of  the  cyclone.  These  nimble  forerunners 
have  been  observed  8oo  miles  in  advance  of  a  storm.  They  sometimes  cau- 
tion the  mariner,  before  his  barometer  gives  any  intimation  of  the  approaching 
tempest. 


CLOUDS 


245 


Cumulus  clouds  derive  their  name  from  the  fact  that  they  are 
heaped  up,  like  vast  mountains  towering  one  upon  another. 
They  are  often  of  glistening  whiteness.  They  abound  in  the 
tropics,  and  frequently  appear  in  the  sky  of  temperate  latitudes 
during  the  summer,  when  evaporation  is  rapid. 

Of  all  cloud  forms  they  are  perhaps  the  grandest.     Out  of 


CUMULO-STRATLS,   KNOXVILLE,   TENN. 

them  darts  the  lightning  which  makes  our  thunder  storms  so 
magnificent. 

Stratus  clouds  appear  in  the  shape  of  long  layers  or  ribbons. 
They  are  seen  most  frequently  in  the  evening,  and,  when  tinged 
by  the  rays  of  the  setting  sun,  they  form  those  islets  of  gold 
which  render  the  sunset  sky  so  beautiful. 

The  compound  clouds  combine  the  features  of  the  simple 
ones  from  which  they  are  named. 

The  Cirro-cumulus  is  made  up  of  fleecy  masses  of  cirrus  which 
roll  themselves  up  into  rounded  shapes.  These  cause  the 
mottled  appearance  commonly  known  as  a  "mackerel  sky." 


246 


MOISTURE   OF   THE   AIR 


The  Cirro-stratus  consists  of  layers  of  cirrus  clouds.  They 
are  often  so  arranged  as  to  resemble  a  shoal  of  fishes,  all  swim- 
ming parallel  to  one  another.  This  cloud,  like  the  cirrus,  is 
often  the  precursor  of  storms. 

The  Cumulo-stratus  is  formed  of  heaped  clouds  resting  on 
layer  clouds.     Like  the  cumulus,  its  general  mass  is  often  quite 


CUMTLUS   AND    NlMBUS,    SEASCAPE 

(United  States  Weather  Bureau.) 

dark  and  threatening,  while  its  edges  are  bright  with  sunshine 
that  is  behind  the  clouds. 

The  Nimbus  is  simply  a  cloud  of  any  kind  from  which  rain 
falls.  Heaped  clouds,  and  curls  and  layers  blend  together,  lose 
their  characteristic  features,  and  form  one  dense  leaden  mass. 
It  often  overspreads  the  whole  heavens. 

When  clouds  rest  on  the  tops  of  mountains,  they  are  actually 
in  contact  with  the  earth ;  often  indeed  they  are  below  the  sum- 
mit of  the  mountain.  Their  average  elevation,  however,  is  about 
half  a  mile.  At  times  they  cannot  be  less  than  four  or  five 
miles  high. 


Cl.dUDS  247 

The  velocity  of  cloud  movement,  when  accurately  estimated 
by  observers,  is  found  to  be  far  more  rapid  than  we  should  sup- 
pose from  the  apparent  rate  of  the  "passing  cloud."  It  has 
been  found  that  cirro-cunuilus  and  cirrus  clouds  which  seem 
to  be  moving  at  a  leisurely  rate  are  often  traveling  75  to  100 
miles  an  hour. 

This  is  of  very  great  interest,  for  it  indicates  to  us  the  velocity 
of  the  upper  currents  of  the  atmosphere. 

Clouds  screen  the  earth  from  exxessive  heat  in  summer,  while 
as  a  mantle  they  keep  it  warm  in  winter  by  checking  radiation. 

Plants  and  animals  are  distressed  by  the  intense  heat  of  the  noonday  sun. 
But  the  more  powerful  the  ray,  the  more  rapid  is  evaporation..  Soon  vapor 
enough  is  lifted  from  the  earth  to  form  the  mitigating  clouds.  They  over- 
shadow the  land,  and  plants  and  animals  rejoice  in  their  shelter. 


M.-S.  PHYS.  GEOG.  —  1 5 


■RI 


XXIII.    RAIN 

General  Statement.  —  The  first  form  assumed  by  the  moisture 
of  the  upper  air  when  condensed  is  that  of  cloud.  If,  however, 
the  process  of  condensation  continues,  and  vapor  exists  in  abun- 
dance, it  is  easy  to  see  that  the  tiny  water  particles  which  make 
up  the  cloud  will  increase  in  size,  until  they  are  too  heavy  to 
float,  and  will  fall  as  raindrops  to  the  earth. 

The  general  cause  of  rainfall  is  that  a  certain  volume  of  vapor- 
laden  air  has  been  chilled  below  the  dew-point,  so  that  it  has  no 
longer  the  same  capacity  for  moisture  as  before.  This  may  be 
brought  about  in  several  w^ays  :  (i)  The  moist  air  maybe  driven 
against  lofty  mountain  slopes  and  cooled  by  contact;  (2)  it  may 
be  chilled  by  being  mixed  with  a  mass  of  colder  air  ;  (3)  it  may 
be  chilled  by  expansion,  as  when  carried  upward  by  ascending 
currents  of  heated  air,  wafted  over  high  mountains,  or  drawn 
into  the  center  of  a  cyclone.  Expansion  has  the  effect  of  cool- 
ing air  and  condensing  its  vapor.  This  last  cause  produces 
the  heaviest  rainfalls  for  short  periods. 

Distribution  of  Rain.  —  Rain  is  very  unequally  distributed  over 
the  earth. 

(i)   The  rainfall  is  greater  on  land  than  at  sea. 

(2)  It  is  greater  in  mountainous  than  in  level  regions. 

(3)  It  is  greater  in  the  torrid  than    in   any  other  zone. 
The  average  annual  quantity,  at  the  equator  is  eight  feet.     It 

diminishes,  however,  on  either  side  as  we  approach  the  poles. 
This  follows  from  the  fact  that  the  torrid  zone,  being  the  hottest, 
is  that  of  the  greatest  evaporation. 

Dry  air  cools  about  1°  for  each  183  feet  of  ascent;  but  if  moisture  is 
present,  as  soon  as  condensation  takes  place,  the  latent  heat  set  free  reduces 
the  rate  of  cooling. 

249 


250 


REGULA'rORS    OF    RAIM   \l  I  25 1 

These  are  the  general  facts  regarding  the  distribution  of  rain. 
We  must  now  consider  more  in  detail  how  this  distribution  is 
brought  about. 

Regulators  of  Rainfall.  — The  great  regulators  of  rainfall  are 
mountains,  deserts,  and  winds.  Each  of  these  has  an  important 
part  to  perform  in  the  distribution  of  rain  over  the  surface  of 
the  earth. 

Mountains  are  the  great  condensers  of  vapor.  If  mountain 
chains  face  winds  coming  from  the  sea,  the  land  lying  between 
them  and  the  sea  is  well  w'atered.  As  they  rob  the  winds  of 
their  moisture,  not  unfrequently  the  region  lying  beyond  them  is 
rainless. 

Thus  the  Himalayas  face  the  southwest  monsoon,  as  it  comes 
freighted  with  vapor  from  the'  Indian  Ocean.  They  make 
India  one  of  the  most  productive  countries  in  the  world  ;  but 
the  plateaus  lying  to  the  north  of  them  are  almost  rainless.  On 
a  smaller  scale  the  Western  Ghats  act  in  the  same  way.  They, 
too,  lie  in  the  pathway  of  the  monsoons,  and  intercept  and  con- 
dense their  vapors.  The  annual  rainfall  upon  their  tops 
amounts  to  about  260  inches,  while  the  country  on  the  east  of 
them  receives  less  than  30  inches. 

But  perhaps  the  most  striking  illustration  of  the  influence  of 
mountains  upon  rainfall  is  to  be  found  in  the  case  of  the  Khasia 
hills,  on  the  northern  shores  of  the  Bay  of  Bengal.  They  in- 
tercept the  southwest  monsoons  as  they  Come  burdened  with 
vapor  from  the  bay.  The  result  is  that  the  winds,  as  they  slant 
up  the  hills  into  the  higher  and  cooler  air,  have  their  moisture 
at  once  precipitated  as  rain,  of  which  about  500  inches  fall  there 
in  the  year. 

In  South  America  the  influence  of  the  Andes  is  familiar. 
The  northeast  and  southeast  trades  come  from  the  sea  saturated 
with  vapor,  and  so  go  into  the  interior,  rising,  and  cooling,  and 
dispensing  showers  as  they  go,  until  they  reach  the  crest  of  the 
Andes.  Here  the  cold  and  expansion  are  sufficient  to  precipi- 
tate almost  all  the  remaining  moisture.  Thus  the  eastern  side 
of  these  mountains,  within  the  trade-wind  region  (see  Chart  of 


252 


RAIN 


the  Winds),  is  abundantly  watered,  while  the  western  is  dry. 
Hence  it  is  that  Peru  is  a  rainless  country. 

South  of  the  mouth  of  the  Plata,  the  reverse  takes  place. 
There  the  prevailing  winds  are  from  the  west.  They  come  from 
the  Pacific,  reeking  with  moisture,  and  water  the  western  slopes 
of  the  Andes,  causing  the  excessive  rains  of  southern  Chile, 
while  the  eastern  slopes  are  comparatively  dry. 

In  our  own  country  the  Cascade  Range  and  the  Sierra 
Nevada  have  a  similar  influence.  They  lie  in  the  pathway  of 
the  westerly  winds  which  come  loaded  with  moisture  from  the 
Pacific.  They  act  as  condensers,  and  bring  down  the  copious 
showers  which  give  fertility  to  the  Pacific  slope. 

In  moiintainless  areas,  like  the  Dakotas,  rain  and  snow  are  caused  by 
currents  of  cold  air  descending  from  tlie  upper  regions  of  the  atmosphere. 
They  reduce  the  temperature  with  surprising  rapidity.  Pouring  into  a  warm 
atmosphere,  they  condense  its  moisture,  and  a  rainfall  or  snowfall  is  the 
result. 

In  many  cases  deserts  are  the  directors  of  the  winds,  and 
thus  become  regulators  of  the  rainfall. 

India  is  in  a  region  in  which  the  northeast  trade  winds  blow 
over  the  land  and  are  rainless.  Were  it  not  for  the  deserts  of 
central  Asia,  which  have  the  effect  of  drawing  in  the  southwest 
monsoons  (see  p.  224),  India  would  be  as  arid  as  Gobi. 

In  Africa  the  Sahara  produces  the  monsoons  which  blow  from 
the  Indian  Ocean  upon  that  continent.  By  June,  the  desert  is 
heated  sufficiently  to  bring  in  the  sea  winds.  The  rainy  season 
then  begins,  and  lasts  till  late  in  autumn. 

The  periodical  overflow  of  the  Nile  is  due  to  rain  resulting 
from  the  condensation  of  vapor  brought  from  the  sea  by  the 
African  monsoon.  Thus  Egypt  owes  its  fertility  in  some  degree 
to  the  burning  sands  of  the  Sahara. 

North  America  has  its  deserts  and  its  monsoons,  though  they 
are  far  less  marked  than  those  of  the  Old  World. 

The  table-lands  of  Mexico,  Arizona,  the  dry  plains  of  Texas,  New  Mexico, 
and  the  neighboring  regions,  are  heated  by  the  summer  sun  to  such  a  degree, 
that  the  air  resting  upon  them  becomes  rarefied,  and  ascends,  the  cooler  air 


RAINS   CLASSIFIED  253 

from  far  and  near  coming  in  to  restore  the  equilibrium.  Thus  a  southeast 
monsoon  is  created  in  the  Gulf  of  Mexico,  and  a  southwest  one  in  the  Pacific. 
Both  of  these  winds  blow  toward  the  land,  and  bring  the  rains  to  Mexico, 
so  that  one  side  of  that  country  is  watered  from  the  Pacific,  and  the  other 
from  the  Atlantic  Ocean. 

As  a  general  rule  winds  are  dry,  if  they  have  traversed  the 
land  or  if  they  are  journeying  toward  the  equator.  Winds  are 
wet,  if  they  have  traversed  the  sea  or  if  they  are  journeying 
from  the  equator. 

Land  winds  are  dry  for  the  simple  reason  that  they  have  so 
little  opportunity  to  take  up  moisture.  Thus  the  northeast 
monsoons  which  sweep  over  the  inland  regions  of  Asia  are  the 
dry  monsoons.  The  westerly  winds  of  our  own  country,  from' 
the  Sierra  Nevada  to  the  Atlantic,  are  dry  winds.  They  bring 
our  fair  weather. 

Again,  a  wind  that  is  blowing  toward  the  equator  is  dry, 
because,  entering  warmer  latitudes,  it  is  gaining  capacity  for 
moisture  with  every  degree  of  its  progress.  The  trade  winds, 
for  example,  blow  toward  the  equator.  You  perceive,  therefore, 
that  they  are  going  from  cooler  to  warmer  latitudes.  Their 
temperature  is  increased  by  the  way,  and  with  increase  of 
temperature  there  is  increase  of  capacity  for  moisture.  The 
trade  winds,  therefore,  take  up  more  water  from  the  sea  than 
they  return  to  it.     They  are  evaporating  winds. 

.Sea  winds  and  winds  blowing  toward  the  poles  are  rainy. 
The  counter  trades  go  toward  the  poles.  They  are  traveling 
from  warmer  to  cooler  latitudes.  Their  temperature  is  de- 
creased by  the  way,  and  therefore  there  is  a  decrease  in  their 
capacity  for  moisture  ;  they  deposit  more  than  they  take  up. 
They  are,  therefore,  rain  winds. 

Rains  Classified.  —  The  winds  are  classified  according  to  the 
regularity  with  which  they  blow,  as  constant,  variable,  and 
periodical.  It  is  proper,  therefore,  to  classify  the  rains  which 
they  bring  in  the  same  way.  Hence,  according  to  the  nature 
of  the  supplying  winds,  the  rainfall  in  any  given  region  is  con- 
stant, periodical,  or  variable. 


254 


RAIN 


The  constant  rains  are  confined  to  a  belt  near  the  equator, 
about  5°  wide.  In  this  belt  there  are  almost  daily  showers. 
The  cause  is  clear.  The  northeast  and  southeast  trades  meet 
near  the  equator.  They  are  so  completely  saturated  with 
moisture  that  the  sailor  hanging  out  his  clothes  in  the  morn- 
ing, is  often  surprised  to  find  in  the  evening  that  they  have  not 
dried  in  the  least.  Under  the  vertical  rays  of  the  sun  an  as- 
cending current  is  produced  which  carries  the  vapor-laden  air 
into  the  higher  regions  of  the  atmosphere.  Here  the  vapor  is 
cooled  and  condensed  ;  and  hence  the  frequent  thunder  showers 
of  this  region  of  constant  precipitation. 

Within  the  tropics,  to  the  north  and  to  the  south  of  the 
narrow  belt  of  Constant  Rains,  lie  the  zones  of  Periodical 
Rains. 

In  the  New  World  the  periodical  rainfall  is  closely  connected 
with  the  annual  movement  of  the  Equatorial  Calm  Belt  and  its 
accompanying  Cloud  Ring. 

The  Calm  Belt  travels  northward  and  southward,  following 
the  apparent  annual  movement  of  the  sun  in  the  heavens.  It  is 
farthest  south  in  March,  and  farthest  north  in  September. 

During  the  time  that  it  is  passing  over  a  place,  it  gives  to  that 
place  its  rainy  season.  After  it  has  passed,  there  is  scarcely 
a  drop  of  rain  until  it  comes  again. 

Let  us  follow  the  Cloud  Ring  in  its  journey  from  south  to  north,  and  we 
shall  readily  understand  its  movements,  and  the  rainy  seasons  that  depend 
upon  them. 

The  time  is  February;  it  is  then  over  Guayaquil  (Lat.  3°  S.),  and  then  the 
rainy  season  there  is  at  its  height.  It  commences  its  movement  for  the  north 
in  March.  Quitting  the  skies  of  Guayaquil  soon  after,  it  leaves  them  bright 
and  clear  with  the  commencement  of  the  dry  season.  In  a  little  while  it  has 
traveled  as  far  as  latitude  4°  N.  It  then  overshadows  Bogota,  where  the  rains 
begin  in  April  or  May.  In  June  it  is  over  Panama,  and  hence  a  rainy  season 
prevails  there :  and  so  the  Cloud  Ring  continues  on  to  Mexico,  reaching 
Mazatlan,  just  under  tiie  tropic,  about  September,  when  it  commences  its 
march  toward  the  south,  so  as  to  be  again  at  Guayaquil  by  February  or 
March. 

It  is  clear  that  on  its  return  from  north  to  soutli  the  Cloud  Ring  must  give 


KXCESSIVE    AND    DEFICIENT    RAINIAl.l,  255 

to   certain  places   a   second  rainy  season  because,  in  coming  and  going,  it 
passes  over  them  twice. 

In  the  Old  World  the  periodical  rains  are  occasioned  by  the 
monsoons  or  reversed  trades.  For  about  six  months,  in  south- 
ern Asia  and  central  Africa,  copious  rains  fall.  When  the  mon- 
soons change,  the  dry  season  sets  in,  and  scarcely  any  rain  falls 
until  after  six  months,  when  the  wet  monsoon  begins  to  blow 
again. 

Within  the  two  belts  of  Periodical  Rains  the  year  is  divided 
into  rainy  seasons  and  dry. 

In  general  terms,  the  rainy  season  in  the  northern  belt  may  be  said  to  begin 
with  April  and  last  till  October,  while  the  dry  season  extends  from  October 
till  April.  In  the  southern  belt  this  order  is  reversed  —  the  dry  season  lasting 
from  April  till  October,  and  the  season  of  rain  from  October  till  April. 

It  is  not  to  be  supposed  that  during  the  rainy  season  there  is  an  incessant 
fall  of  rain.  In  Mexico,  for  instance,  the  rainy  season  is  the  most  delightful 
portion  of  the  year.  As  a  rule  the  nights  and  mornings  are  clear  and  beautiful, 
and  the  weather  fine,  with  a  few  hours  of  rain  after  three  or  four  o'clock  p.m. 

North  and  south  of  the  belts  of  Periodical  Rains,  the  rains 
become  variable  ;  that  is,  they  are  irregularly  distributed  through 
the  year.  In  some  countries  they  occur  mainly  during  the  sum- 
mer, in  others  during  the  winter;  in  others,  again,  during  the 
spring  and  autumn.  This  condition  prevails  throughout  the 
temperate  regions. 

Excessive  and  Deficient  Rainfall.  —  Owing  to  the  influence  of 
local  causes,  there  are  regions  of  excessive  and  deficient  rainfall. 

The  regions  of  excessive  rainfall,  with  few  exceptions,  lie 
within  or  near  the  tropics.  Cherrapunjee,  in  the  vicinity  of  the 
Khasia  hills  in  India,  receives  annually  about  500,  and  in  some 
years  600,  inches  —  or  a  depth  of  50  feet  —  a  greater  amount, 
so  far  as  we  know,  than  any  other  place  on  the  globe. 

Parts  of  the  British  Isles,  the  coasts  of  Guinea  and  Senegambia.  eastern 
Africa  and  India,  are  all  remarkable  for  their  heavy  rainfall. 

In  the  New  World,  Brazil,  Guiana,  Venezuela,  the  West  India  Islands, 
Central  America,  southern  Chile,  and  the  Pacific  shores  of  Alaska  are  all 
regions  of  excessive  rainfall. 


256 


RAIN 


The  Primitive  Method  of  Ikku.aiion  practiced  by  the  Egyptian  1  i,\^\.ms 

The  water  is  raised  in  vessels  attached  to  "  sweeps  "  with  counter  weights  at  the  opposite 

ends. 


EXCESSIVE   AND   DEFICIENT    RAlNIAl.l.  257 

The  rainless  or  almost  rainless  regions  are  the  great  belt  of 
deserts  extending  across  Africa  and  Asia,  from  the  Atlantic 
nearly  to  the  Pacific ;  the  Great  Basin  in  North  America,  lying 
eastward  of  the  Sierra  Nevada ;  Peru,  together  with  the  north- 
ern part  of  Chile,  portions  of  Argentina  lying  eastward  of  the 
Andes,  and  the  interior  of  Australia. 

Cultivation  in  all  dry  countries  is  carried  on  by  means  of  irrigation.  For 
this  purpose  tanks  liave  been  constructed  in  India  at  vast  e.xpense.  The  Peru- 
vian farmers  avai'  themselves  of  the  mountain  streams  that  are  fed  by  the 
snows  of  the  Andes;  while  the  peasant  of  Egypt,  like  his  forefathers,  supplies 
his  fields  and  gardens  from  the  waters  of  the  Nile.  (For  irrigation  in  United 
States,  see  p.  320.) 


XXIV.    HAIL,  SNOW,  AND  GLACIERS 

Hail.  —  Moisture,  descending  through  the  cold  upper  regions 
of  the  atmosphere,  is  sometimes  frozen  and  becomes  hail  or 
snow. 

When  examined  carefully,  hail  has  been  often  found  to  consist 
of  concentric  layers  of  ice,  incasing  one  another  like  the  layers 
of  an  onion. 

In  size,  hailstones  vary.  At  times  they  are  as  large  as  mar- 
bles, or  even  hens'  eggs,  so  that  severe  hailstorms  may  occasion 
very  great  damage  to  crops. 

The  formation  of  hail  is  not  well  understood.  The  sudden 
ascent  of  moist  air  into  the  cold  upper  regions  of  the  atmosphere 
is  probably  the  most  common  cause  of  this  phenomenon. 

Glaisher,  in  his  balloon  ascension,  found  the  temperature,  at 
the  height  of  three  miles,  i8°  F. ;  at  four,  8°  ;  at  five,  — 2°.  The 
temperature  at  the  surface  was  59°. 

Snow.  —The  moisture  that  falls  from  the  clouds,  frozen  in 
flakes,  is  called  snow.  When  examined,  it  is  usually  found  to 
consist  of  exquisitely  formed  crystals,  which  are  generally  in  the 
shape  of  a  six-pointed  star.     (See  illustration.) 

Snow  rarely  occurs  within  the  limits  of  about  30°  north  and 
south  latitude,  except  on  high  mountain  tops.  It  is  naturally 
more  abundant  as  we  approach  the  poles.  It  is  also  in  general 
more  abundant  where  the  climate  is  inland,  than  where  it  is 
maritime.  Paris  has,  on  an  average,  12  snowy  days  in  the 
year;  St.  Petersburg,  170. 

Snow  is  perpetual,  however,  ev^en  at  the  equator,  upon  all 
heights  greater  than  about  three  miles  above  the  sea  level.  The 
line  above  which  snow  is  always  found  is  called  the  snow  line. 
It  varies  in  altitude  from  many  causes. 

258 


I 


SNOW 


259 


Whatever  tends  to  elevate  the  temperature  of  any  locality 
tends  also  to  elevate  the  snow  line.  Hence  a  low  snow  line 
means  a  cold  climate.  While  at  the  equator  the  snow  line  is 
16,000  feet  high,  at  the  Straits  of  Magellan  it  is  only  about  4000, 
and  in  Norway  about  5000. 

The  use  of  snow  is  twofold :  (i)  it  protects  the  earth  and  the 
crops  planted  in  late  autumn  from  the  intense  cold  and  the 
injurious  effects  of  frost.  Sometimes  there  is  a  difference  of 
40°  between  the  temperature  of  the  ground  a  little  below  the 
surface  and  that  of  the  snow  that  covers  it;  (2)  falling  in  vast 


SiNUU   Crvstals 


quantities  on  the  great  mountain  ranges,  as  the  Himalayas,  the 
Alps,  and  the  Rocky  Mountains,  it  serves  as  a  perpetual  feeder 
of  the  rivers. 

The  quantity  of  snow  that  falls  on  an  extensive  range  of  mountains,  such 
as  the  Alps,  is  very  great.  Aga.ssiz  observed  a  fall  of  57  feet  in  si.x 
months  at  the  Hospice  of  Grimsel,  and  observations  during  twelve  years  near 
the  Pass  of  the  Great  Saint  Bernard  showed  an  annual  snowfall  varying 
from  12  to  44  feet.  It  has  been  estimated  that  the  average  annual 
snowfall  on  the  Alps  amounts  to  60  feet,  which  is  equivalent  to  six  feet 
of  water. 

A  large  part  of  the  snow,  as   already  stated,  gradually    melts   and    flows 


26o 


HAIL,    SNOW,    AND   GLACIERS 


thi'ough  the  river  courses  to  the  sea.  Other,  though  smaller  portions, 
consohdated  into  ice,  descend  the  mountain  slopes  into  the  valleys  as 
glaciers.  Frequently  masses  of  snow  are  loosened  from  their  beds  and 
plunge  down  the  steep  declivities  with  frightful  velocity,  forming  avalanches. 
Sometimes  the  echo  of  a  loud  word  is  enough  to  disturb  an  overhanging 
mass  and  hurl  it  into  the  valley  below. 


Lffkcts  ok  an  Avalanchk 
A  scene  in  the  Selkirk  Mountains  of  British  Columbia. 


Many  instances  are  on  record  of  the  appalling  destruction  wrought  by  this 
scourge  of  the  Alps,  whole  villages  having  been  overwhelmed  and  hundreds 
of  lives  destroyed  by  a  single  avalanche.  Thick  forests  are  the  best  protec- 
tion against  danger  from  this  source,  and  in  former  times  the  penalty  of  death 
has  been  adjudged  against  any  who  should  destroy  a  single  tree  of  the  pro- 
tectinji  barrier. 


GLACIERS 


261 


Glaciers  are  vast  masses  of  ice  either  spreading  out  over  the 
surface,  as  in  Greenland  and  the  Antarctic  regions,  or  filling 
valleys,  as  in  the  Alps  and  other  snow-clad  mountains. 


A  Snow-clad  Summit— Mont  Blanc,  "The  Monarch  of  the  Alps" 

This  mountain  has  an  altitude  of  15,730  feet.     In  the  foreground  is  seen  the  village  of 

Chamounix.     Note  the  glacier  extending  downward  into  the  valley. 

In  regions  where  the  snowfall  exceeds  the  loss  by  melting, 
the  accumulated  snow  gradually  becomes  compacted  by  par- 
tial melting  and  by  the  pressure  of  its  own  weight.  Moreover, 
that  which  occupies  the  higher  levels  gradually  creeps  down- 
ward to  the  lower  —  to  the  edge  of  the  plateau  in  the  case  of 
an  ice  sheet,  or  down  a  valley  in  the  case  of  a  mountain 
glacier. 


262 


HAIL,    SNOW,    AND   GLACIERS 


Should  we  follow  a  ravine  downward  from  a  snow-clad  crest, 
we  should  find  the  snow  growing  more  and  more  solid  under 
our  feet  until  we  reached  the  snow  line.  Below  this  the  com- 
pacted snow  would  appear  as  ice.  Following  the  ravine  to  a 
still  lower  level,  we  should  observe  that  the  ice  mass  filled  it 
from  side  to  side  and  terminated  at  length  among  gardens 
and  pastures,  a  stream  of  water  gushing  from  its  cavernous 
extremity. 

Other  glaciers,  smaller  in  extent,  and  containing  comparatively 
little  ice,  never  reach  the  lower  valleys. 


Mek  de  Glace  — Sea  of  Ice 

This  celebrated  glacier  is  formed  by  the  union  of  several  branches  descending  from  the 

Mont  Blanc  range. 


The  compacted  snow  above  the  snow  line  is  called  the  nhw 
(na-va).  It  is  in  general  about  half  the  density  of  ice,  or  more 
than  three  times  that  of  snow. 

Glacial  Motion.  —  Solid  and  immovable  as  these  mighty 
masses  of  ice  appear,  they  are  really  in  motion.  Long  before 
glacial  motion  was  suspected  by  scientific  men,  it  had  been  known 
to  the  mountaineers  that  blocks  of  stone  lying  upon  the  surface 
of  glaciers  moved  slowly  downward. 

A    large   number   of   carefully  conducted  observations  have 


GLACIAL    MOTION 


263 


been  made,  which  prove  not  only  that  the  glacier  has  motion, 
but  that  its  motion  closely  resembles  that  of  a  river.  It  is 
swiftest  in  the  center,  and  slower,  owing  to  the  friction,  near 
the  sides  and  bottom.  Notwithstanding  this  movement,  the 
termination  of  the  glacier  retains  about  the  same  position  from 
year  to  year,  because  it  is  melted  away  as  fast  as  it  moves 
downward. 


Kkanz  Josef  Glacier,  New  Zealand 
This  glacier  lies  on  the  western  slope  of  the  Southern  Alps.     Its  length  is  8\i,  miles. 


The  rapidity  of  the  motion  of  a  glacier  depends  upon  the 
season  of  the  year,  the  size  of  the  glacier,  and  the  inclination 
of  its  bed.  The  motion  is  more  rapid  in  summer  than  in  win- 
ter, in  the  daytime  than  at  night,  and  in  a  large  and  deep 
glacier  than  in  a  small  one. 

The  average  rate  per  year  for  glaciers  of  the  Alps  varies 
from  25  to  about  100  yards. 

The  middle  of  the  Mer  de  Glace  was  found  by  Tyndall  to 
16 


M.-S.  PHYS.  GEOG. 


264 


HAIL,    SNOW,   AND   GLACIERS 


move  20  to  33  inches  a  day  in  summer.     The    rate   is   about 
half  as  much  in  winter. 

The  following  figures  express  in  yards  the  motion,  during  one  year, 
of  a  row  of  poles  set  in  a  straight  line  across  the  glacier  of  the  Aar,  by 
Professor  Agassiz :  — 

5.    20.   48.    55.    62.    64.    67.   6g.    79.    68.    64.    54.    47.   39.    21.    II.    I. 

The  central  part,  therefore,  moved  about  80  yards  a  year. 

The  great  glaciers  of  Greenland  and  Alaska  move  at  various 
rates,  60  or  more  feet  a  day. 

Some  glaciers,  notably  that  of  the  Rhone,  tell  their  own  tale 
of  their  movement  down  the  valley.     On  their  surface  concen- 


The  Mum  Glacier,  Alaska 

This  great  ice-stream,  which  results  from  the  union  of  many  tributaries,  enters  an  inlet  of 
the  sea.  Its  water  front  is  about  a  mile  wide  and  rises  perpendicularly  250  feet  or 
more.  From  it  masses  of  ice  break  away  which  float  off  as  small  icebergs.  Since  the 
above  photograph  was  taken  the  extremity  of  the  glacier  is  less  accessible  to  tourists 
on  account  of  the  shoaling  of  the  inlet. 

trie  curves  are  seen  bulging  toward  the  lower  end  of  the  glacier. 
These  show,  as  clearly  as  a  line  of  stakes,  the  more  rapid 
movement  of  the  central  portion  of  the  glacier. 

Owing  to  the  slowness  of  glacier  motion,  it  may  be  a  century 
or  more  before  what  is  now  the  upper  end  of  the  glacier  will 
get  to  the  foot  of  the  mountain. 

Theory  of  Glacial  Motion. — Various  theories,  none  of  which 
is  in  all  respects  satisfactory,  have  been  advanced  to  account 


THEORY   OF   GLACIAL    MOTION 


265 


for  glacial  motion  and  the  accompanying  phenomena.  The 
first  thing  to  be  accounted  for  is  the  motion  itself.  Two  causes 
for  this  may  be  given  :  (i)  gravitation  ;  (2)  expansion  within  the 
glacier.  It  is  probable  that  both  these  take  part  in  producing 
the  motion. 

Gravitation,  or   the    weight  of   the    glacier,  would   naturally 
draw  the  mass  down  the 
slopes  of  the  valley. 

E-xpansion  within  the 
glacier  needs  explanation. 
When  the  water  from  the 
melted  surface  of  the 
glacier  percolates  down- 
ward into  the  interior  of 
the  mass,  it  encounters  a 
temperature  of  32°  F.  It 
freezes  and  of  course 
expands.  Its  expansion 
must  take  place  in  the 
direction  of  least  resist- 
ance, which,  owing  to 
gravity,  is  toward  the 
lower  end  of   the  valley. 

The  following  facts 
must  now  be  considered  : 
first,  that  the  ice  of  a 
glacier  accommodates  it- 
self to  the  shape  of  its 
inclosing  valley  very  much  as  a  river  does  to  its  channel ;  and, 
second,  that  after  fracture  its  parts  reunite.  These  phenomena 
are  explained  by  what  is  known  as  regelatiou  or  second  freezing. 
If  we  pound  a  mass  of  ice  into  fragments  and  then  moisten 
the  broken  surfaces,  the  fragments  will  readily  freeze  compactly 
together  again. 

This  is  what  occurs  in  a  glacier.     In  passing  through  narrow 
gorges  it  is    crushed    and    broken,  and    in  ghding   over   steep 


'^s^    •* 


Crossing  Franz  Josef  Glacier,  New  Zealand 
Note  the  irregularities  of  the  surface  in  the  form  of 

pinnacles  which  have  resulted  from  superficial 

melting. 


266 


HAIL,   SNOW,   AND   GLACIERS 


CREV  ASSESS 


irregularities  in  its  bed  it  is  cracked  and  splintered.     The  lower 
parts  break  away  from  the  upper,  and  fissures  of  great  depth 

called  crevasses  are 
formed,  as  shown  in 
the  following  illus- 
tration. 

But  after  the  ice 
/^?*:^~  has  been  thus 
broken  and  splint- 
ered or  sundered  by 
crevasses,  it  re- 
unites and  forms 
one  compact  mass.  The  crevasses  admit  warm  air,  and  their  walls 
are  perhaps  slightly  thawed,  or  the  ice  on  the  top  of  the  glacier 
being  melted,  water 
trickles  down  and 
moistens  the  fractured 
surfaces.  In  this  con- 
dition the  mass  of 
fragments  is  com- 
pressed by  its  con- 
fining valley  walls,  the 
sundered  portions  are 
brought  together 
again,  and  regelation 
occurs. 

Underpressure  ice  melts 
at  a  lower  temperature  than 
32°  Y.  If  a  wire  weighted  at 
each  end  is  caused  to  cut 
through  a  block  of  ice, 
water  will  be  seen  flowing 
round  the  wire,  while,  in 
the  cut  behind  or  above 
the  wire,  it  is  found  to  be 

frozen.     This  experiment  has  an  important  bearing  upon  the  phenomena  of 
glacier   motion.     Pressure   is  obviously   exerted   by  certain    portions  of  the 


A  Crevasse 
This  fissure  was  encountered  in  making  an  ascent  of  the 
Jungfrau,  Switzerland.     From  stereograph.     Used  by 
permission. 


I 


MORAINES 


267 


glacier  upon  others,  especially  when  the  glacier  is  squeezed  within  gorges. 
If  this  pressure  reduces  the  melting  point  from  32°  F.  to  28°,  the  mass  being 
above  the  latter  temperature,  it  is  easy  to  see  how  the  onward  movement  of 
the  glacier  would  be  facilitated  by  reason  of  its  partial  liquefaction. 


Moraines. — The  rocks  and 
debris  brought  down  from  the 
slopes  of  the  ravine  by  the 
action  of  the  frost  and  by 
av'alanches  accumulate  on  the 
sides  of  the  glacier,  forming 
dark  bands  of  earth  and 
stones,  varying  in  size  ac- 
cording to  the  character  of 
the  rock  encountered.  These 
bands  are  called  mot-aines. 
Occurring  at  the  sides  they 
are  called  lateral  moraines. 

At  the  confluence  of  two 
glaciers,  the  moraines  which 
skirt  the  two  sides  that  join 
are  united,  and  form  a  medial 
^moraine.  If  another  glacier 
unites  with  this  again,  a 
second  medial  moraine  is 
formed  in  the  same  man- 
ner. 

The  earth,  stone,  and  bowl- 
ders brought  down  on  the 
glaciers  form,  at  the  lower 
end  of  the  glacier,  where  the 
ice  melts  and  leaves  them, 
immense  deposits  called  tcr- 


In 


Moraines  (a,  b,  c,  d,  e).o¥  the  Mer  de 
Glace 
the  above  cut  it  will  be  seen  that 
the  Glacier  du  Geant  unites  first  with  the 
Glacier  des  Periades,  and  from  their  junc- 
tion the  dotted  line  shows  the  medial 
moraine  formed  from  the  right  moraine  of 
the  G6ant  glacier  and  the  left  moraine  of 
the  Periades.  Where  the  glacier  thus  re- 
inforced receives  the  Glacier  de  L6chaud, 
another  medial  moraine  is  formed;  and  a 
third  where  the  Tal^fre  adds  its  tributary 
stream.  By  the  junction  of  these  is  formed 
the  Mer  de  Glace. 


minal  moraines. 

Bowlders  of  Transportation.  —  In  some  regions  of  the  earth 
the  surface  is  strewn  with  bowlders  derived  from  distant  sources. 
They  evidently  once  formed  a  part  of  an  old  moraine,  and  their 


268  HAIL,    SNOW,   AND    GLACIERS 

presence  is  explained  by  the  transporting  power  of  glaciers. 
As  the  ice  melted  they  were  deposited  in  their  present  positions 
and  sometimes  so  gently  as  to  form  the  so-called  rocking  stones 
that  may  be  swayed  back  and  forth  if  pushed  by  the  hand. 
These  transported  bowlders  vary  greatly  in  size.  They  may 
weigh  hundreds  of  tons,  but  usually  they  diminish  in  size  as  the 


A   TRANSFUKlKli   (jl,H  lAL   BOWLDER,   YELLOWSTONE   NA'WONAL   PaRK 

This  massive  bowlder  of  granite  is  24  feet  long,  20  feet  wide,  and  18  feet  high.  To  have 
reached  its  present  position,  near  Inspiration  Point,  it  must  have  been  carried  from 
30  to  40  miles. 

distance  from  their  origin  increases.  A  belt  of  country  extend- 
ing from  the  Baltic  to  the  Black  Sea  is  strewn  with  bowlders 
rent  from  the  Scandinavian  mountains. 

The  Glacial  Period.  —  The  former  existence  of  extensive  ice 
sheets  over  the  northern  portions  of  Europe  and  North  America 
is  evident.  Among  the  proofs  may  be  cited  the  following  :  the 
occurrence  of  smooth  and  polished  rock  surfaces ;  striations  and 


DRUMLINS,   ESKERS,   AND    KAMES 


269 


grooves  similar  to  those  found  in  regions  known  to  have  been 
glaciated  ;  old  moraines  ;  transported  soils  and  bowlders  ;  valleys 
filled  with  transported  rock  waste  ;  ice-eroded  rock  basins  now 
forming  lakes. 

The  time  of  this  ice  invasion  in  the  earth's  history  dates  from 
an  age  just  preceding  the  probable  advent  of  man.  So  exten- 
sive were  the  altera- 
tions of  surface  fea- 
tures then  produced 
that  sufficient  time  has 
not  yet  elapsed  to  ob- 
literate  the  evidence. 

Drumlins,  Eskers, 
and  Kames. —  In  cer- 
tain glaciated  areas,  as 
in  central  New  York, 
central  and  eastern 
Massachusetts,  and 
southern  Wisconsin, 
there  are  found  hills 
and  ridges  of  glacial 
debris  or  ////  having 
an  oval  or  elongated 
oval  form  and  smooth, 
rounded  surfaces. 
Their  longer  axes  lie 
in  the  direction  of  the 
ice  movement,  as  will 
appear  from  an  ex- 
amination of  the  striae  and  grooves  on  the  neighboring  rocks- 
Such  elevations  have  been  termed  dntuilins.  Their  height  varies, 
but  rarely  exceeds  100  to  200  feet;  their  length  also  varies, 
ranging  from  a  half  a  mile  in  the  short  forms  up  to  a  mile  or 
even  two  miles  in  the  more  elongated  forms.  These  hills  are 
of  a  morainic  character  and  often  constitute  the  most  prominent 
features  of  a  landscape. 


Map   showing    the   Area    of    North    America 

covered  by  ice  in   the  glacial  period 

Salisbury.     Geological  Survey  of  New  Jersey. 


2  70 


HAIL,    SNOW,   AND   GLACIERS 


Glacial  Grooves  at  Kingston,  Iowa  —  Iowa  Geological  Survey 
In  these  groovings  the  movement  of  the  ice  body  in  four  directions  is  recorded. 

Another  topographic  feature  of  glacial  origin  is  seen  in  the 
winding  or  sinuous  deposits  of  washed  sand  and  gravel  which 


Drumlin,  Savannah,  Wayne  County,  New  York 
The  right-hand  end  has  been  notched  by  the  wave  cutting  of  Lake  Iroquois,  the  predeces- 
sor of  Lake  Ontario.     From  photograph  by  Professor  H.  L.  Fairchiid. 


glacip:rs  as  kivkr  sources 


271 


form  well-defined  ridges,  not  often  exceeding  50  feet  in  height 
and  usually  of  less  elevation.  They  are  known  as  cskers.  Their 
origin  is  somewhat  obscure,  but  it  is  thought  that  they  represent 
deposits  of  debris  in  subglacial  streams  flowing  in  tunnels  or 
deposits  in  canyonlike  gorges  cut  in  the  ice  by  stream  wear 
and  melting. 

Closely  related  to  drumlins  and  eskers  are  mounds  or  knolls 
of  sand  and  gravel,  glacial  debris,  which  has  been  more  or 
less  stratified  through  water  action.  These  deposits  have  been 
termed  kames.  The  materials  of  which  they  are  composed 
were  evidently  deposited  adjoining  the  ice  by  streams  issuing 


Side  View  of  Esker,  Pittsford,  New  York 
From  pliotogrgph  by  Professor  H.  L.  Fairchild. 


from  glaciers  and,  whenever  the  ice  melted,  left  in  the  form  of 
mounds. 

Glaciers  as  River  Sources. — The  glacier,  as  it  imperceptibly 
glides  down  the  mountain,  is  melting  all  the  time,  and  the 
traveler  upon  its  rugged  surface  may  hear,  far  down  in  its 
creviced  depths,  the  sound  of  running  water,  which  gathers 
volume  from  a  thousand  trickling  streamlets,  and  at  last  issues 
forth,  the  never  failing  source  of  some  noble  river. 

The  Rhine,  the  Rhone,  and  many  tributaries  of  the  Danube 
and  Po  spring  from   glaciers  in  the  region   around  the   Saint 


2/2 


HAIL,   SNOW,    AND   GLACIERS 


Gothard ;  and  every  one  of  the  hundreds  of  glaciers  found 
among  the  Alps  nourishes  some  stream.  The  Ganges,  in 
India,  leaps  out  from  under  a  glacier,  a  torrent  40  yards  in 
width. 

Distribution  and  Size  of  Glaciers.  —  Glaciers  of  enormous  size 
are  found  in  the  Arctic  and  Antarctic  regions.  In  the  Old 
World  the  grandest  glacier  region  of  the  Temperate  Zone  is 
that  of  the  Himalayas.     The  glacier  of  Bepho,  in  one  of  the 


.'.  (iKoup  OF  Kames,  Mendon  Ponds,  Monroe  County,  New  York 
From  photograph  by  Professor  H.  L.  Fairchild. 

valleys  of  the  Karakoram  range,  is  t,6  miles  in  length  —  about 
four  times  as  long  as  the  Mer  de  Glace  —  and  covers  hundreds 
of  square  miles  in  area.  Many  others  in  the  same  region  are 
of  nearly  equal  extent. 

It  is  estimated  that  the  number  of  large  glaciers  in  the  Alps 
is  about  500,  and  that  the  surface  constantly  covered  by  snow, 
neve,  and  ice  is  more  than  1000  square  miles.  The  thickness 
of  the  Alpine  glaciers  is  believed  to  range  from  200  to  800  feet. 


ICEBERGS 


273 


The  Pyrenees  and  the  Scandinavian  mountains  contain  glaciers, 
and  large  ones  exist  in  the  Caucasus. 

In  the  New  World,  Greenland  and  Alaska  have  glaciers  far 
surpassing  in  magnitude  those  of  the  Old  World.  The  Hum- 
boldt Glacier,  in  Greenland,  is  more  than  60  miles  in  breadth  and 
300  feet  deep.  The  Malaspina  Glacier  of  Alaska,  according  to 
Russell,  has  an  area  approximating  1500  square  miles.  He 
has  described  it  as  "a  vast,  nearly  horizontal  plateau  of  ice." 


A-N    li.KlJKK 


Glaciers  are  also  found  upon  Mount  Shasta,  upon  Mount 
Rainier,  and  in  the  Selkirk  Range  in  Canada.  The  Andes, 
except  at  their  southern  extremity,  are  destitute  of  them. 

As  distinguished  from  valley  glaciers,  continental  glaciers  or 
ice  sheets  cover  the  entire  surface  over  large  areas.  They  are 
great  snow  and  ice  plains  or,  if  sufficiently  elevated,  plateaus. 
At  present  they  occur  in  Greenland  and  the  Antarctic  regions. 
The  ice  sheets  of  the  Glacial  Period  were  undoubtedly  of  this 
type. 

Icebergs.  —  The  glaciers  of  the  polar  regions  are  not  melted 
into  rivers  like  those  of  temperate  latitudes,     Their  lower  ex- 


274  HAIL,    SNOW,  AND    GLACIERS 

tremity,  therefore,  is  pushed  out  into  the  sea,  and  masses,  often 
of  great  size,  are  broken  off  from  time  to  time  by  the  buoyancy 
of  the  water  and  borne  away  by  ocean  currents.  These  are 
called  icebergs. 

On  the  polar  side  of  55°,  soutli,  the  sea,  all  the  way  round  the  earth,  is 
studded  more  or  less  thickly  with  icebergs. 

During  his  Antarctic  voyage  in  1841,  Sir  James  Ross  sailed  450  miles  along 
an  unbroken  barrier  of  ice.  It  stood  180  feet  out  of  the  water,  and  was 
aground  in  water  1500  feet  deep. 

Admiral  D'Urville  fell  in  with  an  ice  mass  off  the  Cape  of  Good  Hope  13 
miles  long  and  100  feet  high.  Maury  met  with  them  as  near  the  equator  as 
37°  south  latitude.  Indeed,  icebergs  come  from  the  unexplored  Antarctic 
regions  in  sufficient  number  to  stud  an  area  as  large  as  the  continent  of  Asia ; 
for  navigation  is  endangered  there  by  ice  throughout  an  area  of  not  less  than 
15,000,000  square  miles. 

On  the  north  side  of  the  equator  icebergs  are  found  only  in  the  Atlantic; 
never  in  the  Pacific  Ocean.  They  drift  out  from  their  nurseries  in  the  polar 
regions  with  the  cold  currents,  which  bear  them  southwardly  until  they  dis- 
appear in  the  warm  waters  of  the  Gulf  Stream.  They  frequently  lodge  on 
the  Banks  of  Newfoundland,  where  they  greatly  imperil  navigation. 


XXV.     ELECTRICAL   AND    OPTICAL    PHENOMENA 

Atmospheric  Electricity.  —  Concerning  the  precise  nature  of 
electricity  we  are  ignorant.  Although  known  only  by  its  mani- 
festations or  effects,  it  has  been  defined  as  a  "powerful  physical 
agent."  Among  the  phenomena  attributed  to  it  are  shocks 
more  or  less  violent,  heating  and  luminosity,  chemical  action, 
attraction  and  repulsion,  etc.  Electricity  is  of  two  kinds,  posi- 
tive and  negative.  The  former  is  that  developed  on  a  glass  rod 
by  rubbing  it  with  a  silk  cloth ;  the  latter  that  developed  on  a  stick 
of  sealing  wax  by  rubbing  it  with  a  flannel  cloth.  Bodies  charged 
with  like  electricity  repel,  while  bodies  charged  with  unlike  elec- 
tricity attract  each  other.  By  the  use  of  suitable  instruments  it 
has  been  shown  that  ordinarily  the  atmosphere  is  charged  posi- 
tively and  that  the  presence  of  electricity  is  by  no  means  confined 
to  showery  weather  or  thunder  storms.  During  cloudy  weather  it 
may  be  either  positive  or  negative,  but  during  thunder  or  snow 
storms  it  may  change  from  one  to  the  other  with  great  rapidity. 

The  electric  discharge  known  as  lightning  is  a  visible  mani- 
festation of  atmospheric  electricity.  It  may  occur  between  a 
charged  cloud  and  the  earth  or  between  two  oppositely  charged 
clouds.  It  would  seem  that  the  cloud  units  or  vapor  particles 
are  individually  electrified  and  that  upon  condensation  into 
drops  the  amount  of  electricity  equivalent  to  that  spread  over 
the  surfaces  of  the  component  vapor  particles  is,  in  the  case  of 
each  drop  formed,  spread  over  a  surface  of  much  less  area. 
From  this  it  follows  that  each  drop  becomes  more  highly 
charged  than  its  component  units  or  is  at  a  \{\g\\Q.x  potent ta I. 

A  cloud  is  formed  of  a  vast  number  of  water  drops.  As  they 
further  unite  by  condensation  the  potential  of  the  cloud  becomes 
still  greater ;'  that  is,  the  amount  of  electricity  for  a  given  sur- 
face area  is  increased  more  and  more.     If,  under  such  condi- 


276 


ELECTRICAL   AND   OPTICAL   PHENOMENA 


tions,  the  cloud  should  approach  the  earth,  a  disruptive  dis- 
charge through  the  intervening  air  may  take  place  or  the  same 
phenomenon  may  occur  upon  the  approach  of  two  oppositely 
charged  clouds. 

Lightning  flashes  are  of  several  kinds  —  stream  lightning,  zig- 
zag lightning,  sheet  lightning,  and  ball  lightning. 
Stream  lightning  consists  of  a  broad,  straight  flash. 
Zigzag    lightning   consists   of    flashes   passing   between    two 
bodies  of  air  or  clouds,  or  between  a  cloud  and  the  earth.     Since 

different  portions  of 
the  air  have  different 
conducting  powers, 
and  the  electricity  fol- 
lows the  path  of  least 
resistance,  the  course 
of  the  lightning  natu- 
rally becomes  zigzag. 
Sometimes  the  flash  is 
forked. 

Sheet  lightning,  fre- 
quently called  heat 
lightning,  appears  as 
a  glow  of  light  illumi- 
nating vast  clouds  and 

ZIGZAG   LIGHTNING,    FROM   A   PHOTOGRAPH  ^^^^       j^^.^^      ^^^^^       ^^ 

the  sky.  It  is  probable  that  this  kind  of  lightning  is  the  reflec- 
tion of  the  lightning  of  some  distant  storm. 

Ball  lightning  appears  in  the  shape  of  globular  masses  of  fire, 
which  explode  with  violence.      It  is  of  rare  occurrence. 

Thunder  is  thought  to  be  occasioned  b}'  the  sudden  rushing  together  of 
the  portions  of  the  atmosphere  that  have  been  divided  by  a  flash  of  lightning. 
It  is  not  often  heard  at  a  greater  distance  than  fourteen  miles.  Occasionally, 
however,  in  level  regions  such  as  the  prairies,  it  may  be  heard  at  a  very  much 
greater  distance. 

The  flash  is  seen  instantaneously,  because  light  travels  about  186,000  miles 
in  a  second.  The  sound  requires  about  five  seconds  to  travel  one  mile. 
Hence  if,  after  seeing  the  lightning,  we  count  the  number  of  seconds,  or  pulse 


THE   AURORA  277 

beats,  until  we  hear  the  thunder,  it  is  easy  to  ascertain  how  near  the  flash  has 
been  to  us. 

In  general  the  electricity  does  not  pass  from  the  air  to  the 
earth,  but  only  from  one  portion  of  the  atmosphere  to  another. 
When  a  discharge  to  the  earth  does  occur,  the  effects  are  often 
very  destructive.  The  strongest  trees,  if  struck,  are  rent  and 
stripped  of  their  branches,  the  sap  being  suddenly  converted 
into  steam,  and  an  explosion  actually  taking  place.  Animals 
and  men  who  are  struck  are  almost  always  killed. 

The  Aurora.  —  Another  phenomenon,  in  which  atmospheric 
electricity  apparently  plays  an  important  part,  is  the  illumina- 
tion, often  a  magnificent  display  of  color,  frequently  seen  near 
the  polar  regions  of  the  earth.  It  takes  on  a  variety  of  forms. 
Sometimes  it  is  simply  an  arch  of  light  spanning  the  sky  from 
east  to  west  near  the  horizon,  with  quivering  streamers  of  white, 
green,  or  crimson  light,  shooting  fitfully  to  the  zenith.  Some- 
times mere  masses  of  colored  light  are  observed.  Again  the 
whole  heavens  are  flushed. 

In  the  northern  hemisphere  it  is  called  the  aurora  boiralis 
{"  Northern  Lights  ") ;  in  the  southern  hemisphere,  the  aurora 
australis  ("  Southern  Lights  ").  Of  the  two  displays  the'former 
is  better  known.  The  zone  of  its  greatest  brilliancy  is  slightly 
irregular,  lying,  for  the  most  part,  between  the  parallels  of  60° 
and  70°  north  latitude.  It  follows  roughly  the  Arctic  shore 
line  of  the  Eastern  Hemisphere,  but  in  the  Western  Hemisphere 
it  passes  southeast  from  Alaska  to  Hudson  Bay,  thence  south  of 
Greenland  and  Iceland  to  the  northern  shores  of  Scandinavia. 

Auroras  are  more  frequent  as  we  approach  the  poles.  Within 
the  tropics  they  are  almost  unknown.  Their  law  of  distribution 
seems  to  be  the  reverse  of  that  which  governs  the  distribution 
of  lightning. 

The  following  facts  show  that  the  aurora  is  an  electrical 
phenomenon:  — 

(i)  The  delicate  shades  of  rose,  purple,  and  violet,  which  characterize  the 
more  brilliant  auroras,  can  be  produced  experimentally  by  passing  currents  of 
electricity  through  vacua  in  Geissler  tubes  or  receivers. 


2/8 


ELECTRICAL   AND   OPTICAL   PHENOMENA 


It  has  been  computed,  from  observations  of  a  large  number  of  auroras,  that 
the  beams  do  not  usually  approach  nearer  to  the  earth's  surface  than  50  miles, 
and  sometimes  extend  from  it  to  the  distance  of  more  than  250.  At  such 
altitudes  the  atmosphere  must  necessarily  be  very  attenuated,  like  that  through 
which  the  electricity  is  passed  in  the  experiments  alluded  to. 

(2)  Direct  evidence  of  the  electric  character  of  the  aurora  is  found  in  the 
effect  produced  upon  telegraph  wires  during  an  auroral  display.  The  aurora 
has  sometimes  caused  the  instruments  to  work,  as  though  it  had  been  a  battery. 
Sometimes  it  completely  interrupts  their  work. 

(3)  The  magnetic  needle,  also,  is  frequently  disturbed  during  auroras  in  a 
degree  corresponding  to  their  brilliancy. 

Saint  Elmos  Fire.  —  In  storms  at  sea  the  masts  and  yards 
of  the  ship  are  sometimes  tipped  with   balls  of   electric  light. 

They  are  due  to  elec- 
tricity passing  without 
noise,  when  the  clouds 
are  low,  between  the 
clouds  and  the  tips  of 
the  spars  of  the  ship. 
Optical  Phenomena. 
—  The  most  impor- 
tant of  all  the  optical 
phenomena  connected 
with  the  atmosphere 
is  also  the  most  com- 
mon. It  is  the  diffu- 
sion of  light.  This  is 
brought  about  by  reflection  and  refraction.  By  the  former, 
light  is  propagated  from  particle  to  particle  in  the  atmosphere. 
By  the  latter,  it  is  retained  above  the  horizon  when  the  sun  has 
actually  gone  down,  and  it  is  bent  into  the  atmosphere  before 
he  has  actually  risen  above  the  horizon. 

Refraction  and  reflection  give  rise  to  the  exquisite  variety  of 
colors  which  deck  the  morning  and  evening  sky.  They  also 
occasion  the  phenomena  of  rainbows,  parhelia  (commonly  called 
sundogs  or  mock  suns),  paraselenae  (or  moondogs),  halos,  and 
miragre. 


Saint  Elmo's  Fire 


A 


OPTICAL   PHENOMENA  279 

The  rainbow  is  an  arch  of  colored  light  which  spans  the  heavens  during  a 
storm.  It  is  seen  only  when  the  sun  is  shining  at  the  same  time  that  rain 
is  falling.  The  descending  drops  separate  the  white  sunlight  into  its  ele- 
mentary colors. 

Hales  are  rings  of  prismatic  colors  round  the  sun  or  moon.  They  are  really 
circular  rainbows,  probably  due  to  the  refracting  power  of  the  ice  crystals  com- 
posing cirrus  clouds. 

Mirage.  Another  effect  of  refraction  and  reflection  is  commonly  called 
iiiirage.  It  is  often  observed  in  the  desert.  Distant  villages  seem  under  its  in- 
fluence to  be  near  to  the  spectator  or  to  be  suspended  in  the  heavens  above. 
Sometimes  the  traveler  thinks  he  is  approaching  a  pool  of  sparkling  water,  and 
hastens  to  quench  his  thirst,  when  he  finds  that  he  has  been  pursuing  a  mirage. 
Mirage  is  also  observed  at  sea.  distant  ships  being  seen  elevated  above  their 
true  position,  or  even  inverted  in  the  air. 


M.-S.  I'HVS.  GEOG.  —  1 7 


PART    v.— LIFE 

XXVI.     ANIMALS    AND    PLANTS:    THEIR 
RELATIONS   AND    DISTRIBUTION 

Inorganic  and  Organic  Bodies.  —  In  the  preceding  chapters  at- 
tention has  been  especially  directed  to  the  land,  the  water,  and 
the  air.  They  constitute  the  inorganic  or  lifeless  portions  of  the 
earth.  The  following  pages  treat  of  living  bodies,  including  Man 
himself.  As  such  bodies  are  possessed  of  parts  adapted  to  certain 
ends,  —  for  example,  lungs  for  breathing,  feet  for  walking,  eyes  for 
seeing, — they  are  said  to  possess  organs  having  certain  func- 
tions, hence  all  such  bodies  are  organic.  It  is  customary,  there- 
fore, to  speak  of  mineral  matter  as  inorganic  and  of  living  matter, 
or  that  formed  through  the  process  of  living,  as  organic. 

Of  living  things  two  grand  divisions  are  recognized  :  plants 
and  animals.  In  the  study  of  Physical  Geography  it  is  necessary 
to  consider,  first,  the  relations  of  each  of  these  divisions  to  the 
other ;  and  secondly,  their  distribution  and  its  causes. 

Animals  and  Plants.  —  In  their  higher  forms  animals  and 
plants  are  easily  recognized,  but  lower  in  the  scale  of  life  the 
distinguishing  characters  of  each  become  less  marked  until 
eventually  forms  are  encountered  which  are  recognized  as  ani- 
mals or  plants  with  the  greatest  difficulty  and  at  times  with  much 
uncertainty. 

The  higher  animals  differ  from  the  higher  plants  in  many 
particulars,  among  which  mention  may  be  made  of  the  following  : 
They  have  a  nervous  system  ;  they  are  not  fixed  in  position,  but 
possess  the  power  of  voluntary  motion  ;  they  have  an  internal 
cavity  adapted  to  the  digestion  of  solid  food.  The  higher  plants, 
on  the  other  hand,  are  without  a  nervous  system  ;  they  are  fixed 

280 


ANIMALS   AND    PLANTS 


281 


in  j5osition,  that  is,  the}'  are  without  the  power  of  voluntary 
motion  ;  and  their  nourishment,  unlike  that  of  animals,  being 
liquid  or  gaseous,  does  not  require  a  digestive  cavity.  In  con- 
sequence of  these  distinctions  common  animals  and  plants  are 


Victoria  Regia 

rarely  confused.  When,  however,  the  lower  forms  of  animals 
are  reached,  especially  those  which  are  attached  or  fixed  to  for- 
eign objects  during  the  whole  or  a  part  of  their  lives,  then  there  is 
great  danger  of  mistaking  them  for  plants.  The  sea  anemone 
and  the  coral  polyp,  for  instance,  are  both  plantlike  in  appear- 
ance, the  spreading  tentacles  about  their  mouths  presenting  a 
flowerlikc  fringe. 


282  ANIMALS   AND   PLANTS 

Plants,  in  general,  differ  from  animals  in  their  power  of  trans- 
forming inorganic  matter  into  living  matter.  Animals  do  not 
possess  that  power.  Hence  for  their  food  animals  are  dependent, 
either  directly  or  indirectly,  upon  plants.  Animals  feeding  upon 
plants  are  herbivorous ;  those  feeding  upon  other  animals  are 
carnivorous.  Where  there  is  neither  grass  nor  other  vegetable 
growth,  herbivorous  animals  cannot  live;  and  where  they  are 
not  found,  carnivorous  animals,  which  feed  upon  them,  cannot 
exist  for  want  of  a  food  supply. 

General  Facts  concerning  Distribution.  —  It  is  a  familiar  fact 
that  the  same  kinds  of  plants  and  animals  are  not  found  every- 
where. Some  forms  are  widely  distributed,  others  are  restricted 
to  very  narrow  limits.  The  region  within  which  any  plant  or 
animal  is  found  is  commonly  called  its  geographical  range.  The 
dandelion  and  buttercup  blossom  even  amid  the  glaciers  of 
Greenland.  The  orange,  the  date,  and  banana  grow  only  within 
or  near  the  tropics.  The  gigantic  water  lily  called  the  Victoria 
Regia  has  been  found  only  in  the  basins  of  the  Amazon  and 
Orinoco. 

Range  Dependent  on  Climate.  —  Certain  climatic  conditions 
render  it  possible  or  impossible  for  the  various  species  of  living 
forms  to  exist.  Of  these  conditions  by  far  the  most  important 
are  temperature  and  moisture. 

The  peculiar  plants  and  animals  of  the  torrid  zone  would  ob- 
viously die,  if  placed  amid  the  cold  of  the  Arctic  circle ;  while 
it  is  equally  certain  that  the  polar  bear  and  his  associates  would 
become  extinct,  if  they  were  exposed  to  the  scorching  heat  of 
the  tropics. 

The  early  geological  history  of  the  globe  furnishes  striking  illustrations  of 
this  principle.  The  entire  assemblage  of  animals  that  we  now  lincl  upon  the 
earth  did  not  simultaneously  spring  into  existence.  Those  species  first  ap- 
peared which  were  suited  by  existing  climatic  conditions.  Low  forms  of  ani- 
mal life  prevailed  at  first,  and  then  higher  and  higher  successively,  until  such 
conditions  arose  as  were  favorable  to  the  life  of  Man.  and  then,  at  length,  his 
creation  took  place. 

Moreover,  many  of  the  animals  that  once  abounded  have  entirely  disap- 
peared.    Their  existence  is  attested  only  by  fossil  remains.     Lynxes,  bears, 


MODIFICATIONS    BY   CLIMATE  283 

ami  hyenas  once  roamed  over  the  fields  of  England,  and  crocodiles  swarmed 
in  its  rivers;  huge  mastodons,  larger  than  the  modern  elephant,  flourished  on 
what  are  now  the  banks  of  the  Hudson,  and  browsed  amid  the  forests  of  Si- 
beria. Their  tusks  are  dug  up  at  the  mouth  of  the  Lena  and  upon  the  islands 
of  New  Siberia,  in  such  quantities  as  to  form  an  article  of  regular  commerce, 
under  the  name  "  fossil  ivory."  The  climatic  conditions  favorable  to  their 
existence  have  ceased,  and  their  race  has  therefore  ])ecome  extinct. 

Modifications  by  Climate.  —  It  would  follow  as  a  natural  con- 
clusion from  the  fact  that  plant  and  animal  life  are  largely  de- 
pendent on  physical  conditions,  that  changes  in  these  conditions 
should  bring  about  changes  in  the  plants  and  animals  affected 
by  them.  Such  we  find  to  be  the  fact.  Modifications  of  a  very 
extraordinary  nature  can  be  affected  by  varying  the  "  environ- 
ment"  of  a  plant  or  animal,  and  allowing  the  new  environment 
to  be  permanent  during  a  sufficient  length  of  time.  Many  of 
our  most  valuable  food  plants  have  been  thus  transformed.  The 
grains  in  general  are  believed  to  have  been  originally  wild 
grasses. 

Our  own  Indian  corn  presents  a  very  interesting  illustration  of 
climatic  modification  in  a  vegetable  form.  In  the  South  and  the 
Northwest  it  often  attains  the  height  of  12  to  15  feet.  As  we 
advance  northward  through  its  belt  of  cultivation,  along  the  At- 
lantic slope,  its  height  diminishes,  until,  in  New  England,  it  is 
not  usually  more  than  about  five  feet  high.  Again,  the  appearance 
and  quality  of  its  grain  have  been  singularly  modified.  It  is  a 
familiar  fact  that  we  have  a  number  of  varieties,  field  corn,  sweet 
corn,  pop  corn,  with  white,  yellow,  brown,  and  even  black  grains. 

Similar  illustrations  might  be  given  of  the  modifications  of 
animal  forms  by  changes  in  their  physical  conditions.  The 
Shetland  pony  and  the  race  horse  came  from  one  original  stock. 
The  terrier,  the  greyhound,  and  the  mastiff  had  a  common 
parentage. 

Zones  of  Vegetation.  —  Since  the  extent  of  the  geographical 
range  of  plants  depends  mainly  on  temperature  and  moisture,  it 
follows  that  the  surface  of  the  earth  may  be  divided  into  zones  of 
vegetation.     These  will  correspond  more  or  less  closely  with  the 


284  ANIMALS   AND    PLANTS 

zones  of  temperature.  They  will  of  course  be  defined  not  by  lines 
of  latitude,  but  by  lines  of  heat,  or  isotherms. 

The  principle  of  division  is  this,  that  within  belts  or  zones 
having  a  certain  average  annual  temperature,  certain  plant 
growths  will  flourish  ;  beyond  the  limits  of  such  zones  these 
characteristic  forms  disappear,  and  others  are  found  which  are 
suited  to  the  prevailing  temperature.  Thus  each  zone  has  its 
characteristic  forms  of  plant  life. 

Although  in  naming  the  zones  of  vegetation  the  same  terms 
are  employed  as  in  the  ordinary  divisions  by  lines  of  latitude,  it 
should  be  borne  in  mind  that  the  signification  of  the  terms  has 
been  slightly  changed  in  order  to  accord  with  lines  of  tempera- 
tnre. 

Horizontal  Zones.  —  The  surface  of  the  earth  may  be  divided 
into  the  following  horizontal  zones  of  vegetation:  (i)  an  equa- 
torial zone  ;  (2)  two  temperate  zones  ;  (3)  two  polar  zones. 

The  Equatorial  Zone  extends  north  and  south  of  the  equator, 
and  is  bounded  by  the  annual  isotherms  of  70°.  It  is  the  zone 
of  greatest  heat  and  most  abundant  moisture,  and  consequently 
of  most  luxuriant  vegetation. 

The  characteristic  growth  of  this  belt  is  that  of  the  palms. 
The  trees  do  not  lose  their  leaves  in  winter. 

The  Temperate  Zones  extend  northward  and  southward  of 
the  equatorial,  and  are  bounded  by  the  isotherms  of  32°F.  Here 
the  tropical  palms  disappear,  or  are  replaced  by  dwarfed  repre- 
sentatives of  the  family. 

The  characteristic  forms  are  those  of  the  deciduous  forest 
trees,  —  those  which  shed  their  leaves  in  autumn  and  renew 
them  again  in  spring,  —  of  which  the  oak,  the  chestnut,  and 
others  belonging  to  our  own  forests  are  familiar  examples. 

The  colder  parts  of  these  zones  are  marked  by  the  abundance 
of  conifers  (pines,  larches  and  spruce,  and  juniper  trees). 

The  Polar  Zones  extend  north  and  south  from  the  temperate. 
Within  them  the  average  annual  temperature  is  not  higher  than 
32°F.,  and  in  many  portions  it  is  below  5°.  The  warmer  parts  of 
these  zones  contain  vast  forests  of  spruce,  pine,  and  larch.     The 


HoKTZONTAl.   ZONKS 


285 


A  Group  of  Date  Palms 
A  scene  in  the  town  of  Luxor  on  the  Nile. 


colder   portions    are    characterized    by    the  growth  of  dwarfed 
birch,  alder,  and  willow  trees.     But  beyond  certain  limits  trees 


286 


ANIMALS   AND   PLANTS 


wholly  disappear,  and  only  the  lower  forms  of  plant  life, 
mosses  and  lichens,  remain. 

Vertical  Zones.  —  Since,  by  ascending  sufficiently  high,  even 
in  equatorial  regions,  one  can  pass  through  every  variety  of 
climate,  torrid,  temperate,  and  frigid,  it  is  evident  that  there 
must  be  vertical  as  well  as  horizontal  zones  of  vegetation. 

On  the  lower  slope  of  the  Andes,  for  example,  are  found 
regions  of  palms  and  bananas,  tree  ferns  and  vines.  These 
correspond  to  the  zone  of  equatorial  vegetation.  Higher  up  are 
encountered  the  deciduous  trees  of  the  temperate  zone.     Still 

farther      up 

if  \  there  is  a  re- 

7   JlI\.3^.''\.  ^ion  closely  re- 

S    ■••.-A^:/|^.Tos; ;.  A      Region  of  Lichens.  semblillg      the 

'^''WSS^^^^^Z^^^^-  Arctic    zone: 

I .  ^  2^^^  ^£^^'^^\  ^'^^^^^  Region.  Conifers  are 

^'    ""iSSlfSlW'Si^^  the   prevailing 

.i  ^^*^  ^  9^  s;/^^5^f^  Limit  of  ordinary  large  trees       type,  while  de- 

i  y  \\A''\l^^'^*f\\^lVt(^'^^^^^'^^^^^'^^  ciduous     trees 

S  'y^^^J'^^^'i'y)^^^^^  are   represent- 

y  ixl.^il^^A^:02^^^:^}^  Regionof  Palms  cd   by    shrubs 

~  <  t^--?  /-'  ''^'  --^■^^'-.iv  ^^.^''■g.-,., and      dwarfed 

Vertical  Zones  of  Vegetation 

specimens. 
Near  the  snow  line  trees  of  every  kind  disappear,  and  mosses 
and  lichens  are  the  only  forms  of  vegetation  that  can  with- 
stand the  perpetual  cold. 

The  Flora  of  the  Sea.  —  The  flora  of  the  sea  differs  from  that 
of  the  land  in  color.  It  is  less  inclined  to  green.  The  plants 
of  the  sea  are  brown  and  yellow,  pink  and  purple,  green, 
orange,  and  violet,  with  all  intermediate  shades. 

The  vegetation  of  the  sea  has,  like  that  of  the  land,  a  vertical 
and  a  horizontal  distribution.  Both  are  determined  mainly  by 
the  temperature  of  the  water  and  the  nature  of  the  sea  bed. 

In  the  deepest  parts  of  the  ocean  nothing  but  microscopic 
forms  of  vegetable  life  of  the  simplest  kind  (called  diatoms) 
occur.     The  smaller  algae  or  seaweeds  scarcely  exist  below  the 

i 


THE   FLORA   OF    FHE   SEA  287 

depth  of  300  feet ;  the  larger  are  not  found  deeper  than  about 
60  feet  below  the  surface.  The  horizontal  range  of  many 
marine  plants  is  coextensive  with  the  sea.  Others,  like  land 
plants,  have  limited  ranges. 

Among  the  most  interesting  kinds  of  algae  are  the  Macrocystis 
pyrifcra,  the  H  Unnllcea  utilis,  and  the  Gulf  Weed. 

The  Macrocystis  pyrifera  measures  700  feet  in  length.  Tliis  weed  is  Hlce 
a  cord.  It  attaches  itself  to  the  rocks,  and  grows  from  the  bottom  in  the 
littoral  waters  of  many  covmtries,  and  especially  along  the  northwest  coast  of 
America. 

Few,  if  any,  forms  of  vegetation  have  a  wider  geographical  range  than  this 
weed.  After  all  traces  of  plant  life  on  the  land  have  ceased,  on  approaching 
the  poles,  it  is  still  found  flourishing  in  the  water. 

The  WUrinllcEa  utilis  grows  in  the  waters  of  the  Falkland  Islands  and  ad- 
joining regions.  The  surf  often  twists  it  into  cables  several  hundred  feet  long 
and  as  thick  as  the  human  body.  This,  like  the  Macrocystis  pyrifera,  fastens 
itself  to  the  rocks,  in  stormy  waters,  with  such  tenacity  that  sometimes, 
in  the  attempt  to  tear  it  away,  large  bowlders  are  brought  up  adhering  to  its 
roots. 

Plants  of  this  species  surround  Kerguelen  Land  with  such  a  tangled  mass 
that  rowboats  find  it  difiicult  to  get  through  it.  The  Straits  of  Magellan  are 
so  thick  with  these  weeds  that  they  fouled  the  rudder  and  so  entangled  the 
propellers  of  the  first  steam  vessels  that  passed  through  these  waters  as 
seriously  to  interfere  with  the  navigation. 

Among  the  most  widely  distributed  forms  of  marine  vegetation  is  the  Gulf 
Weed  {Fiicus  nataiis).  It  is  not  known  whether  it  grows  at  the  bottom  or 
near  the  surface  of  the  sea.  It  is  always  found  afloat,  living  and  growing,  but 
without  any  signs  of  roots.  It  lies  so  thick  in  the  Sargasso  Sea  as  completely 
to  hide  the  waters  in  many  places  and  give  the  sea  the  appearance  of  a  drowned 
meadow. 


XXVII.    THE  DISTRIBUTION  OF  USEFUL  PLANTS 

Food  Plants.  —  It  will  be  of  interest  to  consider  the  geo- 
graphical distribution  of  those  plants  that  are  of  the  greatest 
importance  to  man.  Of  these,  the  grains  or  cereals,  as  they 
are  called  (barley,  rye,  wheat,  Indian  corn,  rice,  and  millet), 
deserve  first  attention.  Certain  of  them  have,  of  all  plants,  the 
widest  geographical  range. 

Barley  is  cultivated  in  Europe  as  high  as  70°  north  latitude, 
and  on  the  Asiatic  table-lands  at  an  elevation  of  13,000  feet. 

Rye  will  grow  in  all  regions  between  67°  north  and  south 
latitude. 

Wheat  has  a  range  almost  equal  to  that  of  rye.  It  ripens  in 
North  America  as  far  as  latitude  55",  and  in  Europe,  owing  to 
the  influence  of  tempering  winds  and  currents,  as  far  as  latitude 
64^.  In  Mexico  and  the  Andean  region  its  culture  begins  at 
the  height  of  about  2500  feet  and  is  successful  as  high  as 
10,000.  Upon  the  Himalayas  it  is  cultivated  as  high  as  12,000 
feet  above  the  sea. 

Indian  corn  will  grow  and  ripen  in  the  open  air,  from  the 
parallel  of  45°  or  50°  north  to  the  corresponding  parallel  south. 
Its  range  embraces  two  thirds  of  the  earth's  surface.  In  the 
torrid  zone  neither  wheat  nor  Indian  corn  do  well  at  the  sea 
level,  though  they  j^roduce  finely  on  the  mountain  sides. 

Rice  is  limited  in  its  geographical  range  by  the  parallels  of 
45°  north  and  35°  south.  This  belt  covers  more  than  half  the 
surface  of  the  earth.  The  plant  thrives  best  in  low  and 
swampy  ground,  and  is  the  chief  cereal  cultivated  in  China  and 
japan.  Its  grain  is  the  principal  article  of  food  for  one  third 
of  the  entire  human  race. 

Millet  is  the  most  prolific  of  the  cereals.  It  is  adapted  better 
than  any  other   to   the  vicissitudes  of   a  tropical    climate.      In 

288 


FOOD    PLANTS 


289 


Egypt,  Arabia,  Turkey,  and  Italy  it  is  an  important  article  of 
food,  and  in  India  it,  and  not  rice,  is  the  staple  food  grain. 

Nearly  allied  to  the  cereals  as  an  article  of  diet  is  the  potato. 
It  has  a  range  almost  equal  to  that  of  barley.  It  is  probably  a 
native  of  Chile  or  Peru,  but  will  grow  in  Iceland. 

In  the  ]o\v.  damp,  and  hot  portions  c^f  the  ecjuatorial  region 


Bkeadfrlm  r 

wheat  and  corn  are  replaced  by  rice  and  the  banana,  manioc  or 
mandioca,  and  the  breadfruit. 

The  banana,  indigenous  in  the  regions  of  intertropical  Amer- 
ica, is,  as  an  article  of  food  for  the  masses,  what  rice  is  to  the 
Hindu,  the  potato  to  the  Irish,  and  wheat  to  the  European. 
An  acre  of  ground  planted  in  bananas  requires  less  cultivation 
and  yields  more  abundantly  than  any  other  food  plant.  Hum- 
boldt estimated  the  yield  to  exceed  that  of  the  potato  44  times. 


290 


THE   DISTRIBUTION   OF   USEFUL   PLANTS 


and  that  of  wheat  133  times.  The  banana  flourishes  4000  feet 
above  the  sea. 

Manioc  or  Mandioca  is  a  native  of  South  America.  It  is  also  extensively 
grown  in  Africa  and  other  tropical  regions.  Its  large  turniplike  root,  dried 
and  grated,  is  known  as  cassava,  and  purified  as  tapioca.  It  is  an  article  of 
food  for  a  large  part  of  the  population  of  South  America. 

Breadfruit  is  characteristic  of  the  islands  of  the  Pacific.  Its  fruit  furnishes 
the  natives  with  food  somewhat  resembling  bread. 

Sugar  cane,  so  far  as  we  know  its  history,  seems  to  have  been  a  native  of 
India  or  China.     It  grows  in  the  warm  latitudes  of  every  continent. 

Beverage  Plants.  — The  chief  plants  which  yield  beverages,  tea, 

coffee,  and  cacao,  are 
grown  in  warm  re- 
gions ;  tea  in  China 
and  Japan,  India, 
and  Ceylon  ;  coffee 
in  southern  Asia, 
central  Africa,  and 
the  tropical  portions 
of  North  and  South 
America.  Cacao  is 
a  native  of  the  trop- 
ical regions  of  North 
and  South  America. 
Spices  and  Narcot- 
ics.—  The  geograph- 
ical range  of  the 
spices,  such  as  cin- 
namon, nutmeg,  gin- 
ger, pepper,  cloves, 
and  allspice,  or  pi- 
mento, is  narrow. 
It  is  confined  to  a 
few  degrees  north 
The  East  Indies  are  specially  the 


NUTMEi; 


and  south  of  the  equator, 
region  of  the  spices. 

The  important  narcotics,  tobacco  and  opium,  are  natives  of 


PLANTS  USED  FOR  CLOIHING  29 1 

warm  regions,  but  their  geographical  range  extends  into  the 
temperate  zones. 

Plants  used  for  Clothing.  —  The  principal  plants  which  are 
used  for  textile  fabrics  and  clothing  are  cotton,  flax,  and  hemp. 

Cotton,  the  most  important  of  them  all,  will  grow  and  mature 
well  at  moderate  heights,  anywhere  between  the  parallels  of 
37.^°  north  and  south.  This  belt  being  75°  of  latitude  broad, 
and  extending  entirely  round  the  earth  where  its  circumference 
is  largest,  gives  for  this  plant  a  geographical  range  that  em- 
braces more  than  half  the  earth's  surface. 

The  United  States,  Brazil,  India,  and  Egypt  are  the  chief 
cotton-growing  countries. 

Flax  and  hemp  are  confined  to  the  climates  of  the  temperate 
zone,  and  are  brought  to  their  greatest  perfection  between  the 
parallels  of  25°  and  50°  north. 

The  Medicinal  Plants,  such  as  yield  sarsaparilla,  jalap,  castor 
oil,  quinine,  gums,  and  balsams,  are  almost  all  indigenous  to 
the  torrid  zone. 

Foremost  among  them  stands  the  cinchona,  from  which 
quinine  is  obtained.  Is  is  a  native  of  the  eastern  slopes  of  the 
Andes,  flourishing  in  a  belt  that  extends  through  Bolivia,  Peru, 
and  Equador,  from  3000  to  9000  feet  above  the  sea  level.  It 
has  been  successfully  acclimatized  in  India. 

Useful  Trees.  —  The  ornamental  woods  and  dyewoods,  such 
as  mahogany,  rosewood,  sandalwood,  and  logwood,  are  confined 
to  the  torrid  zone.  The  oak,  walnut,  chestnut,  maple,  ash,  with 
pines,  firs,  and  cedars,  belong  to  the  cooler  latitudes. 

The  geographical  range  of  the  oak  extends  from  the  tropics 
to  the  verge  of  the  frigid  zone.  The  timber  trees  of  the  tem- 
perate zone  are  replaced  in  the  torrid  by  the  teak  and  bamboo. 


XXVIII.     THE    DISTRIBUTION    OF    ANIMALS 

General  Statements.  —  Animals,  like  plants,  require  a  certain 
temperature  for  the  maintenance  of  their  life.  Furthermore, 
no  animal  except  Man  can  inhabit  regions  in  which  nature  does 
not  spontaneously  provide  for  it  suitable  food  ;  and  hence  the 
fauna  of  every  country  is  dependent  on  its  flora.  For  these  two 
reasons  the  distribution  of  animals,  like  that  of  plants,  depends 
mainly  upon  climate. 

Zones  of  Animal  Life.  —  In  view  of  this  fact  it  is  usual  to 
divide  the  earth's  surface,  in  relation  to  its  fauna,  into  the  equa- 
torial, temperate,  and  polar  zones,  as  has  been  done  in  treating 
of  the  distribution  of  plants. 

The  Equatorial  Zone  is  characterized  by  the  abundance  of  its 
forms  of  animal  life.  It  is  the  zone  of  lions,  tigers,  rhinoceroses, 
elephants,  camels,  crocodiles,  poisonous  serpents,  and  birds  of 
the  most  brilliant  plumage. 

The  temperate  zones,  on  the  other  hand,  are  distinguished  by 
the  number  of  their  useful  animals,  such  as  the  ox,  cow,  horse, 
sheep,  and  goat.  The  eagle,  turkey,  and  pheasant  are  among 
the  birds.  In  coloring,  the  animals  of  temperate  regions  are  far 
less  brilliant  than  those  of  the  Equatorial  Zone. 

In  the  Arctic  regions  (for  of  the  Antarctic  we  know  little)  are 
found  the  fewest  species,  although  the  individuals  are  numerous. 
The  reindeer,  musk  ox,  white  and  brown  bear,  wolves,  white 
foxes,  and  sables  are  the  chief  land  animals.  The  seal,  walrus, 
and  whale  frequent  the  waters.  Reptiles  are  unknown.  Ducks 
and  gulls  abound. 

Zoological  Regions.  —  It  is  obvious  that  any  division  of  the 
earth's  surface  into  zones  characterized  by  peculiar  fauna  and 
flora  is  necessarily  far  from   exact.      Although   the  distribution 

292 


I 


ZOOLOGICAL   REGIONS 


293 


of  life  on  the  globe  is  mainly  dependent  on  climate,  it  is  not  so 
altogether. 

For,  in  the  first  place,  many  species  overlap,  being  found  in 
more  than  one  zone. 
The  dog  is  the  com- 
panion of  Man  in 
every  zone ;  sugar 
cane  grows  in  both 
torrid  and  temperate 
regions. 

And  in  the  second 
place,  however  alike 
in  climate  different 
portions  of  the 
earth's  surface  may 
be,  they  do  not  nec- 
essarily have  the 
same  flora  and  fauna. 
The  isotherms  of 
the  United  States 
traverse  also  the 
Empire  of  China. 
Yet  there  are  marked 
differences  between 
the  forms  of  plant 
and  animal  life  which 
characterize  the  two 
regions.  The  iso- 
therms of  68°  F.  pass 
through  Australia, 
South  America, 
China,  and  the  Gulf  region  of  the  United  States.  But  the  vege- 
tation and  animal  life  of  these  regions  are  strikingly  diverse. 

From  these  considerations  scientific  men  have  been  led  to  seek 
a  mode  of  division  more  in  harmony  with  existing  facts  than  that 
represented  by  zones,  and  the  plan    proposed  by  the  eminent 


Chimpanzee 

From   photograph.      Used   by  permission  of  the  New 
York  Zoological  Society. 


(294) 


30      Longitade       60 


130      Greenwich      150 


(29S) 


296 


THE    DISTRIBUTION    OF   ANIMALS 


naturalist  Sclater,    and   more   exactly  defined  by  Mr.  Wallace, 
seems  to  be  the  most  satisfactory  thus  far  devised. 

According  to  this  division  the  surface  of  the  earth  is  made 
up  of  six  regions,  each  of  which  has  certain  forms  of  life 
peculiarly  its  own  and  not  found  elsewhere,  although  it  may  have 


Barbaky  Lion 
From  photograph.     Used  by  permission  of  the  New  York  Zoological  Society. 

many  species  in  common  with  other  regions.  The  following 
are  the  names  of  the  regions  with  their  leading  characteristic 
forms. 

(i)  The  NortJicni  Old  World  Region  includes  all  of  Europe, 
all  temperate  Asia  north  of  the  Himalayas,  and  northern  Africa 
down  to  the  Tropic  of  Cancer.  Here  we  find  the  bear,  wolf, 
deer,  horse,  cow,  and  camel,  the  wild  goats,  the  eagle,  the  corn- 
crake, and  bustard. 

Peculiar  to  this  region  are  almost  all  the  known  species  of 
goats  and  sheep,  moles  and  dormice  ;  and  among  birds  the  night- 
ingales, magpies,  and  almost  the  entire  group  of  pheasants. 

(2)  The  Ethiopian  or  African  Region  Qmhr2iCQs>  Africa  south  of 
the  Tropic  of  Cancer,  southern  Arabia,  and  the  island  of  Madagas- 


ZOOLOGICAL    REGIONS 


297 


car.  Here  we  lose  sight  of  certain  forms  familiar  in  the  Northern 
Old  World  Region,  bears,  deer,  moles,  and  true  pigs  ;  and  camels 
and  goats,  except  in  the  desert  regions,  are  equally  wanting. 

Peculiar  forms  are  the  gorilla,  chimpanzee,  and  baboon,  the 
hippopotamus  and  giraffe,  the  guinea  fowls,  most  of  the  weaver 
birds,  and  the  secretary  bird. 


HirPOPOTAMLS 

From  photograph.     Used  by  permission  of  the  New  York  Zoological  Society. 

Madagascar  and  the  neighboring  islands,  though  classed  as  parts  of  the 
Ethiopian  region,  have  a  fauna  peculiar  to  themselves.  This  insular  sub- 
region  is  one  of  the  most  wonderful  in  the  world  from  a  zoological  point  of 
view.  It  is  especially  characterized  by  the  abundance  of  lemurs  (nocturnal 
animals  somewhat  resembling  monkeys,  but  very  small)  :  while  most  of  the 
groups  in  which  Africa  is  especially  rich  —  apes,  lions,  leopards,  giraffes,  ante- 
lopes, and  elephants  —  are  wholly  wanting.  Some  of  the  birds  are  entirely 
unlike  all  other  known  species. 

(3)  The  Indian  Region  comprises  India,  Indo-China,  and  the 
East  Indian  Islands  as  far  as  the  Strait  of  Macassar. 

Peculiar  to  this  region  are  the  orang-outang,  thetiger.tbe  honey 
bear,  the  civet,  and  flying  lemurs  ;  and  among  the  bright-feathered 


298 


•IIIK    DISIRIBUTION    OF   ANIMALS 


birds,  the  argus  pheasant,  the  peacock,  the  trogon,  and  the  curi- 
ous little  tailor  birds. 

(4)  The  Aiistralian  Region  consists  of  Australia,  New  Zealand, 
Polynesia,  and  those  of  the  Malayan  islands  that  lie  east  of  the 
Strait  of  Macassar. 

This  region  has  a  fauna  of  marked  peculiarity.     It  is  notable 

for  the  absence  of 
forms  elsewhere  al- 
most universal.  The 
higher  mammalia  of 
other  regions  are  re- 
placed by  mammals 
(such  as  the  duck 
mole)  that  lay  eggs  ; 
and  by  marsupials 
(that  is,  animals  with 
a  pouch  for  holding 
their  young).  Of 
these  none  are  found 
elsewhere,  except  the 
opossum  of  North 
and  South  America. 
Among  the  marsu- 
pials of  Australia  are 
the  kangaroo,  the  tree 
kangaroo,  and  the 
wombat. 

The  bird  life  of 
this  region  is  rich  in 
handsome  and  peculiar  forms,  such  as  the  beautiful  bird  of 
paradise,  the  crimson  lory,  the  lyre  bird,  the  bower  bird,  the 
emu,  and  the  cassowary. 

(5)    The  North  American  Region  includes  North  America  and 
adjacent  islands  north  of  the  Tropic  of  Cancer. 

The  fauna  of    this  area  and  that  of- the  Old  World  region 
present  marked  dissimilarities.      Here  we   do    not  find  native 


THREE-HORNEM    GlKAllh 

Copyright,  1905,  by  New  York  Zoological  Society.   U.sed 
l)y  permission. 


ZOOLOC.ICAL    REGIONS 


299 


the  horses,  asses,  cows,  sheep,  pigs,  hedgehogs,  and  dormice 
of  the  Old  World.  They  are  replaced  by  the  bison  (nearly 
extinct),    raccoons,    opossums   (marsupial),    prairie    dogs,    and 


From  photograph.     Used  by  permission  of  the  New  York  Zoological  Society. 


skunks.  The  thrushes,  wrens,  robins,  and  finches  are  rep- 
resented by  new  families. 

Among  animals  peculiar  to  this  region  are  the  grizzly  bear, 
the  pouched  rat,  the  mocking  bird,  the  blue  jay,  the  blue  crow, 
and  the  rattlesnake. 

It  is  hardly  necessary  to  say  that  many  Old  World  forms 
have  been  introduced. 

(6)  TJie  South  American  Region  embraces  South  America 
and  that  portion  of  North  America  and  the  outlying  islands 
which  are  south  of  the  Tropic  of  Cancer. 

Of  all  the  regions  this  is  the  most  remarkable  for  the  fewness 
of   the  forms  which  it  contains  in  common  with   others.      No 

M.-S.  PHYS.  GEOG.  —  18 


500 


KAN(.K   OF   DRALHilir   ANIMALS 


301 


horse  or  ass,  ox,  sheep,  or  goat  is  a  native  of  South  America. 
The  wild  cattle  and  horses  which  now  roam  over  its  plains  and 
pampas  are  the  offspring  of  animals  introduced  by  Europeans. 

This  region  is  equally  remarkable  as  containing  a  greater 
number  than  any  other  of  forms  which  are  strictly  its  own. 
Among  these  are  the  sloth,  the  armadillo,  the   llama,  the  alpaca 


l| 


Gklai  (jka\  Kangaroo 
From  photograph.     Used  by  permission  of  the  New  York  Zoological  Society. 

and  chinchilla,  the  blood-sucking  vampire  bat,  the  prehensile- 
tailed  monkey,^  and  the  destructive  boa-constrictor. 

Here  alone  we  find  the  condors,  toucans,  todies,  rheas,  curas- 
sows,  and  mot-mots.  The  forest-clad  slopes  of  the  Andes  are 
alive  with  the  murmur  of  400  species  of  humming  birds,  some 
of  which  pass  their  existence  near  the  limits  of  perpetual  snow. 

Range  of  Draught  Animals.  —  Of  special  interest  is  the  geo- 
graphical range  of  those  animals  which  Man  employs  as  draught 
animals  or  beasts  of  burden. 

The  horse,  the  ass,  and  the  ox,  either  native  or  introduced, 
are    found  wherever    grains   and    grasses    grow.      Beyond    the 

1  Monkeys  whose  tails  are  capable  of  grasping  the  branches  of  trees. 


302 


THE  DISTRIBUTION   OF   ANIMALS 


limits  of  these  food  plants  the  reindeer  and  the  dog  become 
the  draught  animals.  The  reindeer  is  fitted  to  browse  upon 
Arctic    mosses,   and    has   the   instinct   of    searching   for   them 


SiLVEK-rip  Grizzly  Bear 
From  photograph.     Used  by  permission  of  the  New  York  Zoological  Society. 

beneath  the  snow.  He  presents  one  of  the  most  striking 
cases  of  an  animal  adapted  to  the  peculiar  conditions  of  his 
habitat. 

In  the  equatorial  regions  of  the  Old  World  we  find  the  ele- 
phant serving  as  a  beast  of  burden  ;  while  to  the  northward, 
especially  in  desert  regions,  the  camel  and  dromedary  are 
employed. 

The  cushioned  foot  of  tlie  camel  enables  him  to  tread  firmly  upon  the 
shiftint^  sands  of  the  desert,  while  his  capacity  for  carrying  an  extra  supply 
of  water  adapts  him  wonderfully  for  journeying  through  its  dry  and  thirsty 
wilds. 

In  South  America,  where,  to  traverse  the  continent,  the 
traveler  has  to  scale  the  snowy  heights  of  the  Andes,  there  — 


UAXGE   OF    DRAUGiri"    WIMAl.S 


303 


Soirrn  Amf.rican  Condor 
From  photograph.     Used  by  permission  of  the  New  York  Zoological  Society. 


A  Beast  of  Burden 


304 


THE   DISTRIBUTION   OF   ANIMALS 


and  not  in  North  America,  where  the  mountains  have  gaps 
that  the  buffalo  could  cross — was  found  the  llama,  the  camel 
of  the  New  World,  the  only  beast  of  burden  in  use  among  the' 
native  Americans  at  the  time  of  the  discovery  of  the  continent. 


Malay  Tiger 
From  photograph.     Used  hy  permission  of  the  New  Yorlc  Zoological  Society. 

The  llama,  with  the  alpaca  and  vicuna,  which  are  different  species  of  the 
same  genus,  have  their  habitat  along  the  edge  of  the  snow  line  on  the  Andes, 
where  the  atmospheric  pressure  is  not  more  than  eight  or  ten,  instead  of 
fifteen,  pounds  to  the  square  inch. 

This  diminished  pressure  of  the  atmosphere  has  very  marked  effects  upon 
both  man  and  beast.  To  one  from  the  lowlands,  respiration,  in  these  elevated 
regions,  is  difficult.  Mules  are  used  for  the  transportation  of  merchandise  be- 
tween these  places  and  the  seaboard,  but  never  ascend  beyond  a  certain  height. 
At  the  elevation  of  5000  or  6000  feet  they  are  met  by  the  llamas  of  the  table- 
land, and  the  cargoes  are  exchanged. 

Without  the  camel  and  the  llama  Man,  in  the  early  stages  of  civilization, 
could  have  neither  crossed  the  deserts  of  the  Old  World,  nor  scaled  the  cloud- 
capped  mountains  of  the  New. 

Among  the  fastnesses  of  the  Himalayas,  and  upon  the  bleak  heights  of  the 


LIMITED   RANGE   OF   SOME   ANIMALS 


30s 


plateau  of  Tibet,  the  beautiful  m^'  serves  as  a  beast  of  burden.  He  is  to  be 
seen  browsing  at  an  elevation  of  17,000  feet  above  the  sea.  What  the  camel 
is  to  the  Arab,  what  the  llama  is  to  the  Peruvian,  the  yak  is  to  the  native  of 
Tibet. 

Limited  Range  of  Some  Animals.  —  Many  animals  are  con- 
fined to  a  very  narrow  geographical  range  by  causes  that  are 


r\vo-TuEi>  Sloth 
From  photograph.     Used  by  permission  of  the  New  Yoik  Zoological  Society. 

in  some  cases  quite  obscure.  The  little  chinchilla,  with  its 
beautiful  fur,  has  its  habitat  on  the  Andes  of  Chile  and  Peru, 
8000  to  12,000  feet  abov^e  the  sea. 

The  chamois  inhabits  the  belt  of  the  Alps  which  lies  between 
the  trees  and  the  snow  line. 

The  Kashmir  goat,  noted  for  its  fine  wool,  is  restricted  to 
the  valleys  of  the  Himalayas. 

The  ostrich  of  Africa,  the  rhea  of  South  America,  the  emu 
of  Australia,  the  cassowary  of  New  Guinea,  the  aptery.x  of  New 
Zealand,   are  birds   which    neither  fly   nor   swim.     Their  gee 


306  THE   DISTRIBUTION   OF  ANIiMALS 

graphical  range  therefore  is  very  limited.     The  same  was  true 
of  the  dodo  of  Mauritius  and  the  aepyornis  of  Madagascar. 

Animals  of  limited  range  are  the  most  likely  to  become  ex- 
tinct.    The    apteryx   is   nearly   so ;    the    dodo    has   become    so 


boLTH  American  Llama 
From  photograph.     Used  by  permission  of  the  New  York  Zoological  Society. 

within  two  centuries ;  and  the  aepyornis  became  so  at  a  very 
recent  period,  for  one  of  its  eggs  (eight  times  as  large  as  that  of 
an  ostrich)  was  found  and  brought  to  Europe  in  185 1. 

Fauna  of  the  Sea.  —  As  with  the  animals  of  the  land,  so  with 
those  of  the  sea  —  different  species  have  their  geographical 
range,  both  vertical  and  horizontal,  beyond  the  limits  of  which 
the  conditions  necessary  for  their  existence  are  not  found. 
This,  however,  is  less  rigidly  true  with  regard  to  the  fauna 
of  the  sea  than  that  of  the  land.  It  is  quite  obvious  that 
temperature  must  be  the  main  element  which  determines  the 
habitat  of  marine  animals.  Other  matters,  such  as  the  nature 
of  the  sea  bottom,  have  a  minor  influence. 


—b^—J-^' 


sf-^X 


^    3  \%   t  /  ■  -^'  f '  I'll 
i  \l  lis     ^'    \    it 


307 


3o8 


THE   DISTRIBUTION   OF   ANIMALS 


Life  of  Tropical  Waters.  — The  waters  of  the  tropics,  like  the 
shores  which  they  bathe,  teem  with  the  greatest  variety  of 
animal  forms.  Many  of  the  fish  and  crustaceans  are  decked 
with  colors  of  surprising  brilliancy. 

The  sperm  whale  inhabits  the  warm  waters  of  this  zone, 
and  is  most  abundant  in  the  Pacific  Ocean.  Flying  fish,  alba- 
core,  bonito,  and 
sharks  are  all  in- 
habitants of  inter- 
tropical seas.  Pearl 
oysters,  also,  with 
corals  and  sponges, 
are  found  in  this 
belt. 

Life  of  Cooler 
Waters.  —  In  the 
cooler  seas  of  the 
temperate  and 
x\rctic  regions  we 
find  the  greatest 
abundance  of  fish 
that  are  of  value  to 
Man.  All  the  famous  food  fisheries  in  the  world  -  those  of 
the  cod,  the  herring,  the  mackerel,  and  others  —  are  in  the 
waters  of  cold  currents. 


Al'll-.KVX 

From  Nicholson  and  Lyddecker. 


The  Grand  Banks  of  Newfoundland,  the  fisheries  of  the  North  Sea,  and 
those  of  the  Pacific  coasts  of  America.  China,  and  Japan,  all  lie  within  the 
range  of  the  cold  flow  from  the  north.  It  is  to  the  presence  of  the  cold 
current  along  our  Atlantic  seaboard  that  our  own  fish  markets  owe  their 
celebrity. 

The  right  whale  is  found  in  the  cold  waters  of  polar  seas.  Those  of  the 
torrid  zone  are  as  impassable  to  him  as  a  sea  of  flame.  So  true  is  this  that 
the  right  whale  of  the  northern  hemisphere  and  the  right  whale  of  the  south- 
ern are  restricted  each  to  his  own  zone. 

Although  the  seal  may  be  found  in  all  latitudes,  his  favorite  haunts  are 
the  islands  of  Alaska,  the  shores  of  Labrador,  and  the  bays  of  southern 
Chile  and  Argentina.     Other   inhabitants  of  polar  waters  are  the  sea  lion, 


^ 


TlIK    l-I.ORAS    OF    rilK    /(  tOl,0(  ilt  Al .    KKCIONS 


309 


hunted  for  liis  I'lii.  and  llic  walrus,  hunted  for  his  ivory  tusks,  which  are 
superior  to  those  of  the  elephant,  and  the  narwhal,  or  sea  unicorn,  whose 
ivory  horn  is  eight  or  ten   tVet  in  length. 

Various  depths  are  suited  to  various  species  of  marine  animals.  The  reef- 
building  polyp  cannot  flourish  at  a  greater  depth  than  about  150  feet  below 
the  surface.  Lower  down,  in  depths  so  great  as  1500  or  even  2400  fathoms, 
living  forms  are  found,  but  they  are  of  a  low  order — foraminifera,  sponges, 
starfish,  and  mollusks.  The  bathymetrical  range  of  such  creatures  is  surpri.s- 
ingiy  great. 

The  Floras  of  the  Zoological  Regions.  —  The  floia  of  each 
region  may  not  perhaps  be  so  distinctly  marked  as  the  fauna. 


Wtsr  l.MMAN   Boa 
From  photogiapli.     Used  by  permission  of  the  New  Nork  Zoological  Society. 

There  will  naturally  be  much  overlapping,  many  species  being 
very  widely  diffused,  and  some  being  common  to  all  parts  of  the 
globe.  Still,  we  ought  to  find  some  characteristic  floral  peculi- 
arities in  each  region. 

The  Old  World  region  is  the  native  home  of  all  the  cereals 
excepting  maize,  of  the  apricot,  the  cherry,  the  apple,  the  pear, 
the  olive,  the  cork  oak,  and  sycamore  iig. 

The  EtJiiqpiaii  region  has  among  its  peculiar  vegetable  forms 
the  baobab,  the  oil  palm,  and  coffee. 

The  Indian  region  is  characterized  by  the  banyan,  the  fig,  the 
mango,  cinnamon,  the  guttapercha  and  teak  trees,  and  the  sweet 
potato. 


3IO  THE   DISTRIBUTION   OF   ANIMALS 

The  Australian  region  has  a  flora  very  distinct  from  that  of 
all  others.  The  leaves  of  the  trees  are  of  a  peculiar  bluish  green 
hue,  and  strangely  present  their  edges  to  the  sun,  arranging 
themselves  vertically  instead  of  horizontally.  The  eucalyptus 
or  gum  trees,  of  which  there  are  400  varieties,  are  probably 
the  loftiest  trees  in  the  world.  Many  are  400  feet  high.  One 
monster  was  felled  which  measured  480  feet.  The  beefwood 
trees  are  remarkable.  Instead  of  leaves,  of  which  they  have 
none,  they  have  sheaths  inclosing  their  branches.  They  thus 
resemble  in  structure  the  "  horsetail "  with  which  we  are 
familiar. 

The  NortJi  Anierican  region  is  the  native  home  of  the  mag- 
nolia, the  live  oak,  the  Sequoia  gigantca  (giant  trees  of  Cali- 
fornia), and  persimmon.  Nearly  400  species  of  trees  are 
peculiar  to  this  region. 

The  South  American  region  is  distinguished  by  the  multi- 
tude of  its  parasitic  forms.  Peculiar  to  it  are  the  cinchona,  the 
cacao,  the  manioc,  the  potato,  the  sarsaparilla,  the  Victoria  Kegia, 
and  the  passion  flower. 


XXIX.     MAN 

Range  of  Human  Habitation.  —  Man  dwells  in  every  zone  and 
at  nearly  all  altitudes.  He  is  literally  cosmopolitan.  Unlike  the 
irrational  animals,  he  can  to  a  large  extent  overcome  the  force 
of  external  conditions.  He  can  protect  himself  from  the  severity 
of  the  winter's  cold,  and  maintain  his  existence  amid  the  snows 
of  the  Arctic  regions ;  and  on  the  other  hand  he  can  endure  the 
fierceness  of  intertropical  heat.  Thus  his  horizontal  range -is 
almost  unlimited. 

He  has,  again,  an  ample  vertical  range.  The  lowest  place 
where  men  have  established  permanent  dwelling  places  is  in  the 
valley  of  the  Dead  Sea,  1300  feet  below  the  sea.  The  highest 
is  at  the  convent  of  Hanle,  inhabited  by  twenty  Tibetan  monks, 
16,533  feet  above  the  sea.  These  limits  include  a  vertical  range 
of  more  than  three  miles. 

The  Unity  and  Diversity  of  the  Human  Family.  —  Wherever 
Man  is  found,  he  presents  the  same  essential  features  of  body  and 
of  mind.  No  such  differences  sunder  men  as  those  which  exist 
between  the  horse  and  the  lion,  the  eagle  and  the  ostrich.  The 
human  family  is  of  one  blood. 

Still  the  heat  and  cold  to  which  man  is  habitually  exposed,  the 
food  upon  which  he  lives,  and  the  physical  conditions  generally 
by  which  he  is  surrounded  will,  in  the  lapse  of  time,  produce 
certain  effects  upon  his  bodily  and  intellectual  organization. 
Hence  we  find  wide  diversities  characterizing  different  portions" 
of  the  human  family.  Men  differ  in  color,  in  feature,  in  mental 
and  moral  peculiarities,  industrial  habits,  social  and  govern- 
mental institutions. 

Division  into  Races.  —  Some  ethnologists  divide  the  great 
human  family  into  three,  some  into  five,  others  into  six  or  even  a 
larger  number  of  races. 

3" 


(312) 


L.  L.P0ATE3  ENCR'G  CO.,  N.Y. 

(3'3) 


314 


MAN 


The  five  great  races  of  mankind,  as  generally  recognized, 
are  the  Caucasian  or  white,  the  Mongolian  or  yellow,  the  Negro 
or  black,  the  Malay  or  brown,  and  the  Indian  or  red. 

The  Caucasian  Race  derives  its  name  from  the  Caucasus  range 
of  mountains,  because  of  the  tradition  that  the  region  traversed 
by  these  mountains  was  the  birthplace  of  the  race. 

The  chief  divisions  of  the  Caucasians  are:  (i)  the  Indo- 
European,  comprising  the  Hindus,  Persians,  Circassians,  Sla- 
vonians, Teutons,  and 
Celts  ;  and  (2)  the  Sem- 
itic families,  of  whom 
the  Hebrews  and  Arabs 
are  the  most  important. 

The  term  Indo-European 
is  derived  from  the  fact  that 
this  division  of  the  race  has 
established  itself  all  the  way 
from  India  to  the  farthest 
bounds  of  Europe. 

Nine  tenths  of  the  peo- 
ple of  the  United  States, 
as  well  as  all  the  peoples 
of  Europe,  exxept  the 
Lapps,  Finns,  and  Mag- 
yars, and  the  Turks 
proper,  belong  to  the 
Caucasian  race.  Both  of  the  Americas  are  governed  by  it. 
Africa  is  controlled  by  it.  In  Asia,  it  dominates  from  the  shores 
of  the  Mediterranean,  through  Arabia,  and  Persia,  and  along  the 
southern  slopes  of  the  Himalaya  Mountains  beyond  the  banks 
of  the  Brahmaputra. 

The  Caucasians  are  the  most  symmetrical  in  figure,  comely  in 
person,  and  beautiful  in  feature,  of  all  the  branches  of  the  human 
family.  The  numerous  divisions  and  subdivisions  of  the  race 
vary  in  complexion  according  to  the  region  they  occupy.  The 
extremes  are  the  Germans  with  their  flaxen  hair,  blue  eyes,  and 


Caucasian 


THE   MONGOLIAN   RACE 


315 


fair  skin,  and  the  Hindus  with  raven  locks,  black  eyes,  and  olive- 
brown  or  brownish  black  skin.  The  face  of  the  Caucasian  is 
oval,  the  head  ample";  the  hair  full  and  often  curled  or  wavy. 

In  intellect  this  race  ranks  first.  With  very  few  exceptions 
all  the  leading  thinkers  of  the  world  have  been  Caucasians ;  and 
without  any  exception  all  the  great  discoveries  of  recent  times 
have  been  made  by  members  of  this  family. 

To  this  race  has  been  assigned  the  task  of  civilizing  and 
enlightening  the  world. 
Its  social  habits  and  its 
governmental  institu- 
tions, its  educational  sys- 
tems and  its  religious 
views,  are  those  which 
most  conduce  to  the  ele- 
vation and  happiness  of 
mankind. 

Wherever  the  white 
man  establishes  himself 
he  speedily  becomes 
dominant;  while  the  com- 
munities of  other  races 
into  which  he  introduces 
himself  are  commonly 
subjected  to  a  gradual 
process  of  extinction. 

The  Mongolian  Race  derives  its  name  from  the  Asiatic  tribe 
of  Mongols.  The  Chinese,  Indo-Chinese,  Japanese,  Tibetans, 
Samoyedes,  and  Turks  in  Asia,  the  Finns,  Magyars,  and  Lapps 
in  Europe,  and  the  Eskimos  of  the  Arctic  regions  of  North 
America  are  branches  of  this  race. 

The  color  of  the  Mongolian  is  olive-yellow.  His  face  is 
broad,  with  wide  and  flattened  nose,  and  small,  obliquely 
set  eyes.  His  hair  is  straight,  coarse,  and  black.  In  stat- 
ure he  is  somewhat  below  the  ordinary  standard  of  the 
Caucasian. 


Mongolian 


3i6 


MAN 


In  intelligence  and  moral  character  he  ranks  next  to  the 
Caucasian. 

Branches  of  the  Mongolians,  as  the  Eskimo,  are  very  low  in 
the  intellectual  scale.  Not  so  the  Chinese  and  Japanese.  It  is 
true  that,  in  the  past,  they  have  displayed  the  mental  inactivity 
which  marks  the  Mongolian  in  general.  They  remained  for 
ages  just  where  their  ancestors  had  been.  A  great  change, 
however,  is  going  on.     The  establishment  of   a   constitutional 

form  of  government  by 
the  Japanese,  and  their 
adoption  of  many  im- 
l^ortant  features  of 
European  civilization, 
entitle  them  to  rank 
among  the  progressive 
nations  of  the  world. 

The  same  may  be  said 
in  a  less  degree  of  the 
Chinese. 

Something  also  must 
be  said  in  commendation 
of  the  native  civilization 
of  both  these  great  Mon- 
golian communities. 
China  has  had  a  Govern- 
mental system  which  has 
stood  the  test  of  ages.  Japan,  too,  has  been  a  prosperous  and 
well-ordered  state  for  generations  of  which  we  have  no  count. 
In  religion  the  Mongolians  are  generally  Buddhists. 
The  Negro  Race  is  so  called  from  the  color  of  its  skin  (Latin, 
iiigcr,  black).  It  occupies  nearly  the  whole  of  the  African 
continent.  The  hair  of  the  Negro  is  short  and  curly  ;  his  nose 
is  flat,  wide,  and  upturned ;  his  cheek  bones  are  prominent,  and 
his  lips  thick. 

The  moral  and  intellectual  status  of  the  Negro  in  his  native 
land   is  low.     When  brought  into   contact,  however,  with  the 


Nkcro 


THE    MALAY    RACK 


317 


Caucasian  race,  he  shows  himself  capable  of  considerable  ele- 
vation. 

The  native  Australians,  though  classed  by  some  ethnologists  as  a  separate 
race,  may  properly  be  regarded  as  a  branch  of  the  Negro  family.  They  are 
probably  the  most  degraded  members  of  the  human  species.  Before  the 
European  settler  they  are  rapidly  dying  out. 

The  Malay  Race  is  held  by  some  to  be  a  branch  of  the 
Mongolian.  Its  characteristics  are,  however,  sufficiently  marked 
to  entitle  it  to  separate 
classification. 

The  Malays  occupy 
a  part  of  southeastern 
Asia  and  most  of  the 
islands  of  the  Pacific. 
The  Malay  peninsula, 
Sumatra  and  Java, 
Borneo,  Celebes,  For- 
mosa, the  Philippines, 
New  Zealand,  and  the 
Polynesian  Islands,  all 
had  this  race  for  their 
aborigines. 

The  members  of  the 
Malay  race  are  of 
medium  height,  with 
well-proportioned  limbs. 
Their  color  varies  from  olive-yellow  to  brown  or  black.  Their 
hair  is  coarse  and  black. 

Intellectually  and  morally  the  Malayan  is  of  a  low  order. 
Some  of  them,  however,  have  a  written  language  and  a  legal 
code.     They  are  true  sea  rovers,  and  prone  to  piracy. 

The  American  Indians  constitute  what  some  ethnologists 
designate  as  an  offshoot  of  the  MongoHan  race.  At  the  time 
of  Columbus  they  had  spread  all  over  North  and  South 
America. 

Some  of  the  better  known  tribes  are  the  Chippeways,   Da- 


Mai.w 


3i8 


MAN 


kotas,  Apaches,  and  Cherokees  in  North  America ;  the  Caribs, 
the  Araucanians,  and  Patagonians  in  South  America. 

The  American  Indian  is  copper-colored  or  red,  and  therefore 
he  is  often  called  the  Red  man.  His  hair  is  black,  coarse,  and 
straight,  his  cheek  bones  prominent.  In  person  he  is  tall  and 
lithe.  He  is  remarkable  for  his  endurance  of  fatigue  and  his 
disregard   of   pain.     Intellectually  and   morally  he  occupies  a 

medium  position  among 
the  races  of  mankind. 

The  Incas  of  Peru  and 
the  Aztecs  of  Mexico  were 
found  in  a  remarkable  state 
of  civilization  by  Pizarro  and 
Cortez;  and  there  are,  in 
Central  America  and  in  New- 
Mexico  and  Arizona,  interest- 
ing memorials  of  a  long-for- 
gotten civilization  which  had 
its  home  in  those  regions. 

The  Montezumas  of  Mexico 
had  their  halls,  their  acade- 
mies and  schools,  their  zoo- 
logical and  botanical  gardens, 
their  calendar  and  their  monu- 
ments Their  capital,  at  the 
time  of  Cortez,  vied  with  the 
Amekican  Indian  wealthiest  cities  of  Europe. 

Conditions  Favorable  to  Civilization.  —  From  this  brief  re- 
view of  the  races  it  will  be  seen  how  powerful  has  been  the 
influence  of  physical  circumstances  upon  Man.  Some  portions 
of  the  human  family  have  remained  hopelessly  barbarous; 
some  have  received  civilization  from  others ;  and  some,  again, 
have  originated  a  civilization  of  their  own  —  an  iridigcnons  civi- 
lization. Wherever  this  last  has  occurred,  it  has  invariably 
been  neither  at  the  poles,  nor  in  the  hot  lands  of  the  tropics, 
but  rather  in  a  middle  ground  between  the  two.  It  is  here 
that  conditions  best  adapted  to  man's  physical  development 
are  found. 


MAN'S    INFLUENCE    UPON    T'HVSICAL   GE0(JKA1'IIY  319 

An  indigenous  civilization  has  never  had  its  origin  under  the 
blighting  blasts  of  the  Arctic  regions.  Life  there,  from  the 
cradle  to  the  grave,  is  a  continuous  struggle  for  mere  sub- 
sistence. The  body  is  so  pinched  and  starved  by  cold  and 
hunger  as  to  prevent  the  development  of  the  mind. 

Neither  do  the  moist  and  overheated  climates  of  the  torrid 
zone  appear  to  be  favorable  to  mental  development.  There 
the  rainy  season  and  the  constant  heat  dwarf  and  enervate  the 
body.  Cold  may  not  pinch,  nor  hunger  gnaw,  yet  fever  racks  the 
frame  ;  and  the  mind,  in  its  first  and  feeble  steps  toward  civiliza- 
tion, is  crippled  by  the  ills  of  the  body.  Body  and  mind,  more- 
over, lack  in  the  torrid  zone,  by  reason  of  its  superabundant 
productiveness,  the  great  stimulus  to  human  exertion,  —  necessity. 

Man,  to  be  civilized,  must  be  beyond  the  reach  of  climatic 
extremes. 

Man's  Influence  upon  Physical  Geography.  —  While,  however, 
we  notice  the  influence  of  physical  geography  upon  Man,  we 
must  also  notice  the  influence  of  Man  upon  physical  geography. 
Although,  like  the  brutes,  he  is  strongly  impressed  by  his 
material  sunoundings,  he  is  unlike  the  brute  creation  in  this : 
They  cannot  modify  the  conditions  which  surround  them ;  he 
can.  The  methods  to  which  he  resorts  are  mainly  three : 
( I )  Drainage,  (2)  Irrigation,  (3)  Extension  of  the  range  of  useful 
plants  and  animals. 

In  many  cases  skill  and  perseverance  triumph  over  natural 
difificulties  that  seem  insuperable. 

Immense  changes  are  wrought  by  artificial  drainage.  Super- 
fluous water,  instead  of  being  left  to  form  marshes,  saturate 
the  soil,  and  be  taken  up  by  evaporation,  is  carried  off  under- 
ground through  the  drain  pipes ;  consequently,  the  air  is  not 
so  largely  impregnated  with  moisture  as  formerly,  and  the  soil, 
instead  of  being  constantly  chilled  by  evaporation,  is  rendered 
warm,  genial,  and  productive. 

This  result  is  particularly  noticeable  in  England  and  Scot- 
land, where  very  extensive  areas  have  been  drained  and 
brought  under  cultivation. 

M.-S.  I'HYb.  GEOG.  —  I9 


320  MAN 

Holland  has  been  reclaimed  from  the  sea.  The  water  has  been  diked  out ; 
and  many  parts  of  the  country  that  were  the  bottom  of  tiie  sea  are  now  dry 
land,  and  though  below  the  level  of  the  sea,  form  the  home  of  industrious  and 
happy  communities. 

Years  ago  there  were  "  drowned  lands"  along  the  lower  banks  of  the 
Mississippi,  subject  to  overflow,  and  uninhabitable,  embracing  an  area  larger 
in  the  aggregate  than  the  state  of  New  York.  Many  of  these  lands  have  now 
been  reclaimed  by  means  of  levees. 

The  dike  lands  of  Nova  Scotia  and  New  Brunswick  have  been  reclaimed 
from  the  sweeping  tides  of  the  Bay  of  Fundy.  They  are  probably  the  finest 
hay  lands  in  the  world.  Some  of  them  have  been  cropped  200  years.  They 
are  as  sure  to  yield  as  the  fields  of  Egypt. 

By  Man's  agency  in  using  the  waters  of  the  Nile  for  irrigation, 
Egypt  became  in  olden  time  the  granary  of  the  world.  Canals 
conveyed  the  water  to  lands  not  reached  by  the  flood.  And 
to-day  the  Egyptian  peasant  is  using  with  profit  the  devices 
employed  by  his  ancestors  more  than  3000  years  ago.  Sharply 
contrasted  with  these,  as  a  result  of  modern  engineering,  is  the 
great  dam  at  Assuan  by  which  an  ample  water  supply,  for  irri- 
gating purposes,  has  been  afforded  to  a  large  territory.  Much 
of  the  country  yields  three  crops  every  year. 

In  India  and  Ceylon  vast  districts  of  country  are  rendered  fer- 
tile by  the  use  of  reservoirs,  constructed  ages  ago  for  collecting 
water  in  the  rainy  season,  but  even  on  a  larger  scale  by  the 
gigantic  systems  of  irrigation  constructed  by  the  English. 

The  dry  regions  of  our  own  country  also  are  now  largely 
irrigated.  In  Utah,  California,  Arizona,  New  Mexico,  and  other 
far  Western  states  the  wilderness  has  been,  by  this  means,  trans- 
formed into  a  garden.  Some  single  "canals"  with  their  distrib- 
uting channels  carry  water  to  150,000  acres. 

Races  of  men,  species  of  animals,  and  families  of  plants  have 
been  carried  from  one  country  to  another,  and  their  geographi- 
cal range  enlarged. 

Indian  corn,  tobacco,  and  the  potato,  with  many  other  plants, 
the  turkey,  and  other  animals,  were  indigenous  to  America. 
They  have  been  carried  to  the  Old  World  and  acclimated.  On 
the  other  hand,  the  horse  and  cow,  the  sheep,  hog,  goat,  ass,  and 


MAN'S    IMLLKN'CE    Ul'OX    I'lIYSlCAL   tiKoi  IRAl'IIV  3_M 

Other  animals  of  the  Old  World,  with  wheat,  oats,  rye,  barley,  and 
rice,  the  sugar  cane  and  coffee,  and  a  great  variety  of  other 
plants  have  been  transported  to  America. 

A  few  stray  cattle  and  horses,  escaping  to  the  pampas  and 
llanos  of  South  America,  multiplied  exceedingly.  So  wonderfully 
did  they  increase  that,  upon  the  jiampas,  they  were  slaughtered 
by  millions  for  their  hides,  horns,  and  tallow. 


XXX.    GEOGRAPHICAL    DISTRIBUTION    OF  LABOR 

Distribution  of   Labor  Dependent  on  Physical   Geography.  — 

Every  nation  has  industries  peculiar  to  itself.  These,  to  a  large 
extent,  have  their  root  in  geographical  circumstance,  or  in  dif- 
ference of  climate. 

To  show  how  human  labor,  when  unaffected  by  tariffs  and 
untrammeled  by  legislation,  would  naturally  distribute  itself 
over  the  earth  in  obedience  to  geographical  law,  let  us  suppose 
two  families  to  have  been  planted  originally  on  the  earth,  one 
at  the  equator,  the  other  in  the  Arctic  regions.  How  different, 
on  account  of  their  geographical  surroundings,  would  be  their 
occupations  ! 

The  intertropical  family  would  seek  the  shades  of  the  groves, 
pluck  the  ripe  fruit  overhead,  require  little  clothing,  and  be  ex- 
empt from  undergoing  the  hardships  of  toil  to  earn  their  daily 
bread.  With  little  exertion  on  their  part  nature  would  supply 
their  wants. 

The  Arctic  family,  on  the  contrary,  would  be  clothed  with  skins 
and  furs ;  the  earth  would  produce  no  grain  or  vegetables  for 
them.  They  would  live  by  the  chase  and  the  bounties  of  the 
sea. 

Now,  suppose  these  two  families  gradually  to  extend  themselves, 
the  one  toward  the  north,  the  other  toward  the  south,  meeting 
midway  near  the  isotherm  of  50°. 

The  occupations  of  both,  as  they  continued  to  approach  this 
middle  ground,  would  no  longer  be  directed,  on  one  side  mainly 
toward  the  sea,  and  on  the  other  exclusively  to  the  soil  ;  but 
would  become  more  and  more  diversified. 

The  necessities  of  the  southern  family  would  compel  them  to 
resort  to  sundry  active  occupations,  some  to  the  manufacture  of 
clothing,  others  to  the  fabrication  of  implements  for  husbandry  ; 


indusiriils  ok  ruF.  uxri'F.i)  states  323 

others  again  to  seafaring.  Novel  opportunities  would  present 
themselves  to  the  northern  community,  and  induce  them  like- 
wise to  subdivide  their  labor.  They  would  divert  a  portion  of 
it  from  the  sea  and  the  chase,  and  devote  themselves  to  a 
greater  or  less  extent  to  agriculture,  to  the  forest,  the  mine,  and 
the  factory. 

Such  a  diversitv  of  occupation  really  exists  among  men. 
The  middle  latitudes,  embracing  regions  lying  not  far  from  the 
isotherm  of  50°,  form  a  belt  encircling  the  earth,  where  human 
occupations  are  most  diversified.  In  some  parts  of  this  belt  the 
tending  of  flocks  and  herds  and  the  raising  of  stock  are  the 
chief  industrial  pursuits  ;  in  other  parts  agriculture,  in  others 
mining,  manufacturing,  seafaring,  and  lumbering  ;  in  some,  all 
of  these  occupations,  or  several  of  them,  are  combined. 

To  the  south  of  this  middle  ground,  the  attention  of  the  people 
is  devoted  more  and  more  to  the  field  and  the  forest ;  to  the 
north,  more  and  more  to  hunting  and  the  sea. 

Along  this  middle  ground  are  found  the  most  active  seafaring 
and  commercial  peoples  in  the  world,  the  greatest  manufactur- 
ing nations,  and  the  largest  cities. 

Within  its  belt  are  included  most  of  the  United  States,  Japan, 
the  populous  parts  of  China,  and  all  the  great  commercial,  min- 
ing, and  seafaring  communities  of  Europe. 

It  is  now  easily  perceived  that  there  are  geographical  reasons 
why  the  people  of  South  America,  of  Africa,  India,  and  of  the 
tropical  and  subtropical  regions  of  the  earth  should,  in  the  main, 
be  agricultural  or  mining  in  their  industries  rather  than  seafar- 
ing or  manufacturing. 

In  general  it  may  be  laid  down  as  a  rule,  that  the  industries 
of  every  country  are  connected  with  its  geography,  and  that 
human  labor  is  distributed,  largely,  in  obedience  to  certain  phys- 
ical conditions. 

Industries  of  the  United  States.  —  A  brief  survey  of  the  indus- 
tries of  our  own  country  will  serve  well  to  illustrate  this  law  of 
the  geographical  distribution  of  labor. 

Let  us  observe  in  the  first  place  how  the  principle  applies  to 


324  GEOGRAPHICAL    DISTRir.UTIOX    OF    LABOR 

our  various  agricultural  pursuits.  Climate,  of  course,  furnishes 
the  predominant  reason  why  different  products  are  raised  in 
different  parts  of  the  country.  But  we  shall  notice  that  other 
minor  causes  are  not  without  their  influence.  In  the  valley  of 
the  Mississippi,  which  may  be  regarded  as  the  great  agricultural 
region,  there  is  found  as  we  advance  northward  from  Louisiana, 
a  succession  of  climatic  belts,  and  a  corresponding  variety  of 
crops  engaging  the  attention  of  the  husbandman. 

First  of  all,  near  the  borders  of  the  Gulf  of  Mexico,  comes  a 
belt  in  which  sugar  and  rice  are  important  crops.  Leaving  this 
belt,  we  enter  regions,  one  after  another,  specially  adapted  to 
the  cultivation  of  cotton,  tobacco,  corn  and  wheat,  hemp,  the 
grape,  and  orchard  fruits. 

If  the  journey  lie  along  the  Atlantic  slope  from  Florida  to 
Maine,  we  find  a  similar  succession  of  belts  and  products  ;  but 
with  this  striking  difference,  owing  to  the  influence  of  the  sea, 
namely,  that  the  climates  are  milder  and  the  belts  broader. 

In  the  "  Tide-water  Country  "  these  belts  are  so  widened  that 
rice  cultivation  is  carried  up  into  North  Carolina,  cotton  is  raised 
in  Virginia,  and  figs  in  Maryland  —  all  much  farther  north  than 
on  the  west  of  the  Appalachians. 

In  the  tide-water  country  of  Georgia  and  the  Carolinas,  rice 
is  an  important  article  of  cultivation.  There  is  a  geographical 
reason  for  this.  Rice  fields,  in  certain  stages  of  the  crop,  must 
be  flooded,  for  which  purpose  the  tidal  creeks  and  rivers  of  the 
seaboard  afford  excellent  facilities. 

At  the  same  time  Louisiana  has  become  the  first  rice-growing 
state  in  the  Union.  In  the  Mississippi  delta  the  river  is  high 
above  the  cultivated  ground.  Consequently  a  supply  of  water 
can  be  obtained  by  simply  tapping  the  river.  In  the  southwest- 
ern parishes,  away  from  the  river,  and  on  the  coastal  plain  of 
Texas,  large  areas  of  low  and  level  lands  are  irrigated  from  sur- 
face reservoirs  and  wells. 

The  agricultural  pursuits  of  the  Pacific  slope,  owing  to  its 
physical  peculiarities,  differ  from  those  of  the  Atlantic.  No  rice 
or  cotton  is  cultivated.      Hut  the  region  is  unsurpassed  for  its 


INDUSTRIES    or   NEW    EXC.I.AND    AND    (.1  I.F    S  I  A  TKS  325 

wheat  and  fruit  crops  ;  the  olive,  vine,  and  orange  yield  abun- 
dantly, while  stock,  raising  and  wool  growing  are  profitable 
employments. 

Considering  now  the  various  other  industrial  pursuits  of  our 
people,  we  find  it  to  be  the  rule  that  Physical  Geography  has 
largely  determined  how  the  occupants  of  each  section  shall 
employ  themselves. 

Here  we  view  far-reaching  grass-covered  plains  which  naturally 
suggest  the  occupations  of  stock  raising,  dairying,  or  wool  grow- 
ing. Elsewhere  we  traverse  forests  famed  for  lumber,  ship 
timber,  and  naval  stores.  In  yet  another  region  we  observe  that 
attention  is  directed  to  the  great  lakes  or  water  courses  for  fish 
and  fowl ;  or  to  the  interior  of  the  earth  for  minerals ;  or  to 
commerce,  manufacturing,  and  navigation. 

All  these  occupations  are,  it  is  true,  adopted  according  to 
individual  fancy,  yet  they  are  clearly  prompted  and  controlled 
by  geographical  influences. 

Industries  of  New  England  and  Gulf  States  Contrasted.  — 
A  very  striking  illustration  of  the  law  of  geographical  distribu- 
tion of  labor  is  obtained  when  we  contrast  the  leading  occupations 
of  such  widely  separated  sections  of  our  country  as  the  Gulf 
states  and  New  England. 

In  the  former  there  is  no  "  wintry  weather."  The  husband- 
man may  labor  in  the  field  all  the  year  long,  and  the  soil  yields 
abundantly- 

In  New  England,  on  the  other  hand,  the  ground  is  covered 
with  snow,  or  is  frozen  hard,  during  four  or  five  months  in  the 
year.  How  is  New  England  industry  to  ply  its  hand  during  this 
period  ?     It  cannot  till ;  neither  can  it  stand  idle. 

Forests  upon  the  mountains,  ships  upon  the  sea,  quarries  of 
valuable  stone,  and  above  all  factories  of  every  description  fur- 
nish ample  employment  for  the  industrious  population.  New 
England  is  preeminently  devoted  to  manufacturing.  Its  polished 
granites  and  marbles  are  distributed  everywhere  along  the  At- 
lantic seaboard  for  building  and  ornamental  purposes  ;  its  manu- 
factures find  a  market  in  every  part  of  our  own  country  and  are 


326  GEOGRAPHICAL   DISTRIBUTION   OF   LABOR 

exported  to  the  far-distant  seaports  of  China  and  Japan  and  the 
islands  of  the  seas. 

Louisiana,  and  her  sister  Southern  states,  on  the  other  hand, 
want  laborers  for  their  harvests  of  cotton,  corn,  sugar,  rice,  naval 
stores,  hemp,  tobacco,  etc.  There  are,  therefore,  inducements 
peculiar  to  each  of  these  two  sections  which  allure  the  people  of 
one  to  this  branch  of  industry,  the  people  of  the  other  to  that, 
according  to  geographical  conditions.  In  one,  these  inducements 
lead  to  the  sea  and  the  factory ;  in  the  other,  they  point  to  the 
bosom  of  the  earth. 

Mining  and  Manufacturing.  —  If  coal  and  the  useful  metals  are 
found  in  any  region,  manufacturing  interests  will  sooner  or  later 
be  developed.  It  is  in  no  small  degree  owing  to  her  vast  deposits 
of  coal  and  iron  that  Great  Britain  occupies  her  extraordinary 
position  as  a  manufacturing  nation.  Pennsylvania,  Ohio,  Ala- 
bama, Illinois,  the  Virginias,  Maryland,  Michigan,  and  other 
states  similarly  rich  in  the  useful  minerals,  are  actively  engaged 
in  mining  and  metallurgy. 

Fishing  and  Commerce.  — Again,  people  are  maritime  in  their 
habits  from  physical  reasons  ;  partly  because  they  are  adjacent 
to  the  sea,  and  partly  because,  owing  to  the  conditions  which  sur- 
round them, the  bounties  of  the  sea  are  to  them  more  enticing  than 
thebounties  of  the  land.  Hence  it  is  found  that  the  seafaring 
populations  of  the  world  belong  chiefly  to  those  countries  where, 
either  from  the  poverty  of  the  soil,  the  severity  of  the  climate, 
or  the  high  price  of  food,  it  is  easier  for  some  of  the  population 
to  make  a  living  by  braving  the  sea  than  by  delving  on  shore. 

Ships  at  sea  are  not  manned  by  sailors  from  the  Mississippi 
Valley  and  the  Southern  states,  where  lands  are  cheap,  climates 
mild,  and  where  the  soil  is  lavishly  kind  ;  but  rather  by  men 
from  New  England, .Great  Britain,  and  the  countries  of  north- 
western Europe,  where,  largely  on  account  of  geographical  con- 
ditions, the  laborer  finds  it  in  many  cases  easier  to  make  a  living 
at  sea  than  on  shore. 

Commerce  originates  between  nations  to  satisfy  needs.  Arti- 
cles required  for  food  and  shelter,    comfort    or  luxury,   being 


FISHING   AND   COMMERCE  327 

irregularly  distributed  over  the  globe,  it  becomes  necessary  that 
human  industry  should  be  partly  directed  to  the  exchanging  of 
the  natural  and  artificial  products  of  one  region  for  those  of 
another.  To  this  end  many  routes  of  commerce  have  been  es- 
tablished, necessitating  the  investment  of  great  capital  in  rail- 
roads, steamships  and  other  vessels,  and  at  the  same  time  giving 
employment  to  a  vast  multitude  of  people. 


APPENDIX 


XXXI.    PHYSICAL   GEOGRAPHY    AS   A    SCIENCE 

Scope  of  Physical  Geography.  —  The  earth  is  not  young. 
Like  a  hving  being,  it  is  a  product  of  evokition  or  growth.  In 
the  course  of  its  development  it  has  passed  through  many 
stages.  The  interaction  of  sea  and  land,  rock  decay  and  denu- 
dation, transportation  and  deposition  of  sediment,  vulcanicity 
and  glaciation,  elevation  and  subsidence,  earth  folding  and  fault- 
ing, animal  and  plant  life,  have  all  contributed  to  its  present 
form.  Yet  the  earth  as  we  know  it  is  not  a  finished  product ; 
change  and  remodeling  are  still  taking  place ;  the  forces  of  the 
past,  in  varying  degree,  are  still  at  work.  It  is,  however,  as  the 
abode  of  man,  chiefly,  that  the  earth  merits  our  attention.  The 
relation  of  man  to  his  environment  or  surroundings  is  a  practical 
matter,  and  should  we  define  Physical  Geography  as  the  study 
of  the  earth  and  its  phenomena  in  the  present  stage  of  their 
existence  with  special  reference  to  that  relationship,  we  have 
before  us  a  field  of  the  widest  scope. 

The  Relation  of  Physical  Geography  to  Other  Sciences.  —  It  is 
only  by  a  knowledge  of  the  earth  in  its  present  condition  that 
Man  has  been  able  to  interpret  its  past  history.  Physical 
Geography  is,  therefore,  a  most  important  adjunct  to  geology. 
Indeed,  there  is  no  well-marked  line  of  division  between  these 
sciences  which,  in  many  instances,  occupy  common  ground. 
Geology,  however,  is  usually  confined  to  a  consideration  of  the 
history  of  the  earth  and  its  inhabitants  as  recorded  in  the  rocks. 
But  this  seems  arbitrary  in  view  of  the  fact  that  the  earth  is  a 
unit.  It  were  better  that  Physical  Geography  should  constitute 
the  latest  chapter  of  geology. 

328 


HOW    rilVSKAI,   (^.KOC.k.MMIV    SlIOll.l)    RE    STl'DIl  H         329 

Like  geology,  Physical  Geography  rests  iij)on  a  fouiuhition  of 
other  sciences.  To  explain  the  phenomena  of  the  earth  it  has 
oftentimes  been  necessary  to  invoke  assistance  from  astron- 
omy, chemistry,  physics,  zoology,  botany,  and  mineralogy  ;  for 
the  earth  is  one  of  the  planets,  it  consists  of  matter,  it  is  in- 
habited by  animals  and  plants,  and  is,  for  the  most  part,  com- 
posed of  mineral  substances. 

How  Physical  Geography  should  be  Studied.  —  In  the  ele- 
mentary study  of  Physical  (jeography  the  text-book  occupies  an 
important  position.  Not  only  is  such  a  work  a  record  of  the 
observations  and  conclusions  of  those  who  have  made  a  specialty 
of  earth  phenomena,  but  also  a  manual  of  guidance  for  those 
who  desire  to  acquaint  themselves  with  the  subject.  Moreover, 
at  the  outset  the  student  should  understand  that  although  the 
ability  to  memorize  a  text  may  add  much  to  his  information, 
it  is  by  no  means  an  index  of  his  scientific  attainments.  If 
the  best  results  are  to  be  obtained  from  the  study  of  Physical 
Geography,  he  should,  as  far  as  possible,  verify  the  data  and 
conclusions  of  the  author.  By  training  of  that  kind  he  may 
become  competent  to  make  independent  observations  and  from 
them  deduce  proper  conclusions.  Then,  and  not  till  then,  has 
he  reached  that  degree  of  culture  which  is  truly  scientific. 
His  local  or  home  surroundings  become  now  an  ever-present 
field  of  research.  Nowhere  in  the  world  is  the  opportunity 
for  geographic  investigation  denied  him.  Lines  of  investiga- 
tion open  in  many  directions  :  He  may  observe  winds,  clouds, 
rainfall,  temperature,  and  other  weather  conditions  and  note 
their  bearing  upon  climate ;  he  may  study  the  effects  of  rock 
weathering  or  decay  and  the  topographic  features  arising  from 
erosion ;  he  may  face  the  problems  of  stream  dissection,  current 
action,  delta  formation,  cascades  and  waterfalls  in  the  rill 
formed  by  a  passing  shower ;  he  may  learn  something  of 
Nature's  processes  by  observing  the  effects  of  storms  and 
floods.  These  and  many  other  fields  of  inquiry  equally  inviting 
lie  within  the  reach  of  all  students.  Furthermore,  every  local- 
ity has  its  special  phenomena  :  For  example,  wave  action  may 


330  PHYSICAL   GEOGRAPHY    AS    A    S(  H'.NCE 

be  studied  by  those  living  upon  the  sea  coast  or  near  lakes  and 
ponds;  ice  action  by  those  living  in  the  colder  regions  of  the 
earth ;  glaciers  and  glacial  motion  by  those  living  in  Alpine 
regions ;  and  vulcanicity  and  earthquakes  by  those  living  in 
volcanic  regions  or  parts  of  the  earth  subject  to  crustal  disturb- 
ances. 

Maps,  Models,  and  Other  Illustrative  Materials.  —  There  are, 
however,  fields  of  geographic  inquiry  which  ordinarily  lie  be- 
yond the  reach  of  most  students,  as  the  expense  of  investigation 
is  too  great  or  the  region  to  be  examined  too  remote  or  too 
inaccessible.  To  this  class  belong  deep-sea  research,  electro- 
magnetic observations,  Arctic  exploration,  the  investigation  of 
high  mountain  ranges,  the  exploration  of  desert  regions,  and 
the  like.  Such  forms  of  research  can  be  carried  on  only  under 
the  auspices  of  the  government  or  of  well-endowed  private 
institutions.  The  student  of  geographic  tastes  should  embrace 
every  opportunity  to  travel.  There  are  problems  worthy  of  his 
best  thought  and  effort  within  the  boundaries  of  his  own  state. 
But  for  the  elementary  student  this  also  is  usually  impracticable, 
hence  the  necessity  of  a  geographical  collection  in  every  school 
or  college.  This  should  include  a  set  of  the  most  recently 
published  maps  of  the  continents ;  a  good  atlas,  selected  folios, 
atlas  sheets  and  charts  from  the  publications  of  the  United 
States  Geological  Survey  and  the  United  States  Coast  Survey ; 
relief  models  of  the  continents ;  the  Harvard  Geographical 
Models  ;  and  a  relief  globe  such  as  the  Jones  Model.  In  ad- 
dition, if  possible  there  should  be  included  a  set  of  lantern 
slides  or  photographic  views.  Such  illustrations  are  extremely 
valuable  to  the  student,  as  they  convey  to  him  an  exact  im- 
pression of  the  regions  or  phenomena  under  consideration. 
He  should,  moreover,  have  access  to  other  books  than  the 
text,  but  their  number  will  depend  upon  the  resources  of  the 
individual  or  the  school. 

In  higher  institutions  a  similar  equipment,  but  in  an  enlarged 
form,  should  constitute  the  furnishings  of  a  geographic  labora- 
tory.    Here  the  number  of  relief  maps  and  models  should  be 


MAPS,    MODELS,    AND   OIHEK    ILI.ISTR  VIIVK   MAIKRIALS       33 1 

greatly  increased,  especially  by  the  addition  of  duplicates  of  the 
many  excellent  models  prepared  under  the  auspices  of  the 
United  States  Geological  Survey  and  other  departments  of 
the  national  government.  The  collection  of  maps  should  also 
be  made  more  complete,  and  embrace  not  only  political,  but 
topographic  and  geologic  maps  as  well.  If  not  found  in  other 
departments  of  the  institution,  some  of  the  more  common  in- 
struments for  weather  observation  should  be  added,  such  as  a 
mercurial  or  aneroid  barometer,  a  themometer,  a  vane,  anemom- 
eter, and  rain  gauge.  This  laboratory  should  be  furnished 
with  tables  suitable  for  map  work,  cabinets  for  the  storage  of 
maps,  photographs,  and  other  geographic  matter.  While  the 
facilities  afforded  by  such  a  laboratory  may  increase  many  fold 
the  value  of  Physical  Geography  as  a  study,  they  do  not  sup- 
plant the  necessity  of  actual  observation  in  the  field. 


INDEX 


Abyssinia,  plateau  of,  123. 

Aconcagua,  48. 

Active  volcanoes,  50. 

Adirondack  Mountains,  104. 

.■Epyornis,  306. 

Africa,  drainage  of,  169,  170. 

rainfall  of,  252. 

relief  of,  123-126. 
Agonic  lines,  38. 
Agulhas  current,  197. 
Air,  currents  of,  219. 

moisture  of,  239. 

■weight  of,  202. 
Alaska,  climate  of,  213. 
Albacore,  308. 

Alcohol  in  thermometers,  208. 
Aleutian  current,  196. 
Alexandria,  25. 
Algae,  in  hot  springs,  42. 

sea  forms  of,  287. 
Allegheny  plateau,  107. 
Allspice,  290. 
Alluvial  plains,  78. 
Alpaca,  301,  304. 
Alps,  114-116. 
Altai  Mountains,  121. 
Amazon  River,  no. 

description  of,  168. 

no  delta,  150. 
.'\ndes  Mountains,  107-109. 
Anemometer,  218. 
Angle  of  dip,  36. 
Animal  life,  zones  of,  292. 
Animals,  aquatic,  307. 

distribution  of,  292. 

higher.  280. 

lower,  281 

modified  by  climate,  283. 


Antarctic  drift,  196,  197. 
Antarctic  Ocean,  174. 

currents  of,  195. 
Anticline,  87. 
Anti-cyclones,  232. 
Antisana,  108. 
Anti-trades,  221. 
Apennines,  117. 

Appalachian  Mountains,  104-107. 
Apple,  309. 
Apricot,  309. 
Apteryx,  305,308. 
Aquatic  animals,  307. 
Arabia,  121. 
Aral,  Lake,  160,  161. 
Ararat,  121. 
Arctic  Ocean,  173,  174. 

currents  of,  195. 
Argon,  200. 
Argus  pheasant,  298. 
Arica  earthquake,  64. 
Arid  region,  erosion  in,  84.' 
Armadillo,  301. 
Armenia,  121. 
Artesian  wells,  142-144. 

temperature  of,  41. 
Artificial  magnet,  32. 
Ash  trees,  291. 
Ashes,  volcanic,  50,  53. 
Asia,  drainage  of,  169. 

relief  of,  1 19-123. 
Asia  Minor,  121. 
Ass,  301. 
Asteroids,  10,  12. 
Atlantic  coast  tides,  188. 
Atlantic  drift,  213. 
.\tlantic  highlands,  104-107,  T09 
.Atlantic  Oc^an,  174-178. 

333 


334 


INDEX 


Atlantic  Ocean,  currents  of,  193,  194. 
Atlas  Mountains,  123. 
Atmosphere,  70. 

circulation  of,  219. 

composition  of,  200. 
Atmospheric  electricity,  275. 
Atmospheric  pressure,  202. 
Atmospheric  temperature,  206. 
Atolls,  132-135. 
Attractive  power  of  earth,  ^^. 
Aurora  australis,  277. 
Aurora  borealis,  277. 
Australia,  flora  of,  310. 

great  barrier  reef,  132. 

relief  of,  126,  127. 
Australian  Alps,  126,  127. 
Australian  current,  196. 
Autumnal  equinox,  27. 
Avalanche,  260. 
Axis  of  the  earth,  23. 

direction  of,  25. 
Axis  of  elevation,  95. 

Baboon,  297. 

Bad  lands,  84. 

Baikal,  Lake,  164. 

Balkan  Mountains,  116. 

Balsams,  291. 

Baltic  Sea,  climate  of,  213. 

saltness  of,  172. 
Bamboo,  291. 
Banana,  289. 
Banyan,  309. 
Baobab,  309. 
Barbary  lion,  296. 
•Barley,  288. 

Barometer,  mercurial,  203. 
Barrier  islands,  182. 
Barrier  reefs,  132. 
Bars,  148. 
Basin,  165. 

Basins  of  geysers,  42,  43. 
Bath,  temperature   of  springs  at,  41. 
Bay  of  Fundy,  tides  in,  188. 
Bear,  292,  296,  297,  299,  302. 


Beefwood  tree,  310. 

Belted  coastal  plain,  78. 

Bepho,  272. 

Beverage  plants,  290. 

Bird  of  paradise,  298. 

Birds,  292,  300. 

Bison,  299. 

Black  Stream,  196. 

Blanc,  Mont,  116,  261. 

Block  mountains,  88,  102,  104. 

Blue  crow,  299. 

Blue  jay,  299. 

Blue  Mountains,  Australia,  126. 

Boa-constrictor,  301,  309. 

Bolivian  plateau,  82,   108. 

Bonito,  308. 

Bonneville,  Lake,  103,  161-162. 

Boothia,  34. 

Bores,  189. 

Bower  bird,  298. 

Bowlders,  transported,  268. 

Bowlders  of  transportation,  267. 

Brahmaputra,  delta  of,  79. 

Brazil  current,  193. 

Brazilian  highland,  109. 

Breadfruit,  289. 

Breadth  of  wave,  179. 

Breakers,  179,  180. 

Breezes,  land  and  sea,  224. 

Bridge  of  Sighs,  99. 

Bristol  Channel,  tides  in,  189. 

British  Columbia,  climate  of,  213. 

British  Islands,  128—129,  213. 

Broken  plateaus,  83. 

Brown  bear,  292. 

Budapest,  temperature  of  well  at,  41. 

Bustard,  296. 

Cacao,  290,  310. 

Caldera,  29,  161,  162. 

Calendars,  29. 

California  earthquake,  63,  66—69. 

Calms,  belt  of,  223. 

of  Cancer,  223. 

of  Capricorn,  223. 


i 


INDEX 


335 


Calumet-Hecla  mine,  temperature  of, 

40. 
Camel,  292,  296,  302,  303. 
Campagna,  165. 
Cancer,  Tropic  of,  30. 
Canyon,  90,  91. 
Capricorn,  Tropic  of,  31. 
Caracas  earthquake,  65. 
Carbon  dioxide,  200. 
Carbonate  of  lime,  42. 
Carnivorous  animals,  282. 
Carpathian  Mountains,  116. 
Carson  Lakes,  103. 
Cascade,  151. 
Cascade  Mountains,  100. 
Caspian  Sea,  123,  160,  161. 
Cassava,  290. 
Cassiquiare  River,  no. 
Cassowary,  298,  305. 
Castor  oil,  291. 
Catskill  Mountains,  104. 
Caucasian  race,  314. 
Caucasus,  116. 
Cayambe,  108. 
Cayuga  Lake,  156,  160. 
Cedars,  291. 
Centigrade  scale,  209. 
Centrifugal  force,  20,  184. 
Centrosphere,  22. 
Cen'in,  Mont,  85. 
Chaco,  III. 

Chain,  mountain,  85,  86. 
Chamois,  305. 
Change  of  seasons,  29. 
Charleston  earthquake,  63. 
Cherr)',  309. 
Chestnut,  291. 
Chimborazo,  47,  48,  109. 
Chimpanzee,  293. 
China,  plains  of,  123. 
Chinchilla,  301,  305. 
Chottes,  126. 
Cinchona,  291,  310. 
Cinnamon,  290,  309. 
Circulation,  oceanic,  197. 


!  Circulation    of  the  atmosphere,  218, 
219. 

of  water,  139. 
Cirques,  100. 
Cirro-cumulus  cloud,  244. 
Cirrus  cloud,  242,  244. 
Civet,  297. 
Civilization,  318. 
Climate,  210. 

affected  by  ocean  currents,  212 

affected  by  winds,  212. 

at  Werchojansk,  212. 

continental,  211. 

inland,  211. 

insular,  211. 

maritime,  211. 

of  Alaska,  213. 

of  British  Columbia,  213. 

of  Cuba,  216. 

of  England,  213. 

of  Labrador,  213. 

of  Norway,  213. 

of  Oregon,  213. 

of  Orizaba,  216. 

of  Sahara,  212. 
Climatic  belts,  324. 
Clothing,  plants  used  for,  291. 
Cloud,  definition  of,  243. 
Cloud  Ring,  254. 
Clouds,  classes  of,  244. 

formation  of,  201. 
Cloves,  290. 
Coast  line,  72-74. 
Coastal  plains,  76. 
Coffee,  290,  309. 
Colorado,  Grand  Canyon  of,  91. 
Colorado  Plateau,  104. 
Columbia  Plateau,  100. 
Coma,  12. 
Comets,  10,  12. 
Commerce,  326. 

Comstock  lode,  temperature  of,  40. 
Condensation  of  water,  138,  139,  240. 
Condors,  301,  303. 
Conduction,  207. 


336 


INDEX 


Constant  rains,  254. 
Constant  winds,  221. 
Continental  climate,  211. 
Continental  elevation,  91. 
Continental  islands,  128,  129. 
Continental  relief,  95. 
Continents,  70. 
Contraction,  eflfects  of,  86. 
Convection,  206. 
Coral  islands,  130-135. 
Coral,  reefs,  131,  132,  197. 

sand,  178. 
Corals,  308. 
Cork  oak,  309. 
Corn,  324. 
Corncrake,  296. 
Coronado  Beach,  179,  180. 
Cotidal  lines,  186. 
Cotopaxi,  47,  50,  108. 
Cotton,  291,  324. 
Counter  current,  192. 
Counter  trades,  221. 
Cow,  292,  296. 
Crater,  46. 

Crater  Lake,  156,  161. 
Craters,  or  basins,  of  geysers,  43. 
Crest,  mountain,  86. 
Crest  of  wave,  179. 
Crevasse,  266. 
Crimson  lory,  298. 
Crocodiles,  292. 
Crumpling,  86. 
Cuba,  climate  of,  216. 
Cumulo-stratus,  245. 
Cumulus,  243,  245. 
Curassows,  301. 
C'urrent,  Arctic,  213. 
Currents,  ocean,  192-198,  212. 
Curvature  of  the  earth,  18. 
Cut-off,  147. 
Cyclones,  229,  230. 

Dangerous  archipelago,  133, 
Danube  River,  delta.s,  149. 
jetties  of,  148. 


Date  palms,  285. 
Day,  lunar,  183. 

sidereal,  28. 

solar,  28. 
Day  and  night,  lengths  of,  26. 
Dead  Sea,  122,  123,  159,  160. 
Declination,  magnetic,  37. 

of  the  needle,  36. 

variations  in,  38. 
Dee,  tides  of  the,  189. 
Deer,  296. 

Deficient  rainfall,  255. 
Deformation,  crustal,  93. 
Dekkan,  121. 
Delta,  78,  79,  149. 
Delta  plain,  79. 
Delta  shore  lines,  79. 
Dembea,  Lake,  123. 
Density  of  the  earth,  21. 
'Denudation,  77. 
Deposition,  146-150. 
Desert  plateaus,  85. 
Deserts,  regulators  of  rainfall,  252. 
Dew,  241.  '       ~' 

Diastrophic  plateaus,  82. 
Diatoms,  178,  286. 
Dip  of  strata,  77,  78. 
Dip  of  the  needle,  34. 
Dipper,  24. 

Dissected  plateaus,  83. 
Distributaries,  149. 
Distribution  of  animals,  292. 

of  rainfall,  248,  249. 
Diurnal  variations,  38. 
Dodo,  306. 
Dog,  293,  302. 
Doldrums,  223. 
Dormant  volcanoes,  50. 
Dormice,  296. 
Drainage,  165-170,  319. 
Draught  animals,  301. 
Drift,  Antarctic,  196,  197. 

Atlantic,  213. 
Dromedary,  302. 
Drowned  mines,  142. 


INDEX 


337 


Drumlin,  269,  271. 

Dry  season,  255. 

Dublin,  temperature  of,  217. 

Duck  mole,  298 

Ducks,  292. 

Dunes,  126,  227, 

at  Ostend,  184. 
D'Ur\'illa;a  utilis,  287. 
Dust,  in  atmosphere,  200,  201,  206. 

volcanic,  50.  54. 
"Dust  whirlwind,"  254. 
Dyewoods,  291. 

Eagle,  292,  296. 
Earth,  a  magnet,  i^. 

and  the  universe,  17. 

an  oblate  spheroid,  20. 

a  planet,  11. 

attractive  power  of,  :i:i. 

axis  of,  23. 

curvature  of,  18. 

density  of,  21. 

fluidity  of,  45. 

interior  of,  45.   • 

internal  heat  of,  40. 

magnetic  pwles  of,  33. 

magnetism  of,  32. 

motions  of,  23. 

nucleus  of,  22. 

revolution  of,  23,  25. 

rotation  of,  23,  25. 
Earthquakes,  60-69. 

causes  of,  66—69. 

flistribution  of,  65. 

duration  of,  61. 

.sea  waves  caused  by,  63,  64. 
East  Australian  current,  196. 
Ebb  tide,  183. 
Eclipse  of  the  moon,  19. 
Edwards  plateau,  89. 
Egypt,  floods  of,  170. 
Elburz,  Mount,  117. 
Elburz  Mountains,  120. 
Electricity,  atmospheric,  275. 
Electro-magnet,  32. 


Elephants,  292,  302. 
Elevation,  continental,  91. 

effect  of,  216. 
Elton,  Lake,  161. 
Emu,  298,  305. 
luigland,  climate  of,  213. 
Epicentrum,  in  earthquakes,  60. 
Flquator,  23. 

magnetic,  34. 
Equatorial  Calm  Belt,  223. 
Equatorial  current,  192,  193,  194,  196, 

198. 
Equatorial  zone  of  animal  life,  292. 

vegetation,  284. 
Equinox,  autumnal,  27. 

vernal,  26,  207. 
Equinoxes,  76,  27. 
Eratosthenes,  problem  of,  24. 
Eroded  plateaus,  83. 
Erosion,  75,  83,  86,  99,  144-146. 
Eruptions,  volcanid,  51-55. 
Esker,  271. 
Estacado,  Llano,  82. 
Estuaries,  92,  93. 
Eucalyptus,  310. 
Europe,  coast  line,  73. 

drainage  of,  168. 

relief  of,  114-118. 
Evaporation,  138,  139,  239. 
Everest,  Mount,  119. 
Excessive  rainfall,  255. 
Extension  of  plants  and  animals,  319. 
Extinct  volcanoes,  50. 

Fahrenheit  scale,  209. 
Fault,  60,  66. 
Faulting,  86. 
Field   magnetic,  ;^^. 
Figs,  309,  324- 
Finches,  299. 
Fiords,  93,  94,  117. 
Firs,  291. 
Fishing,  326. 
Fissure  springs,  141. 
Fixed  stars,  11. 


338 


INDEX 


Flanks,  mountain,  86. 

Flax,  291. 

Flood  plain,  78. 

Flood  tide,  183. 

Floods,  166. 

Fluidity  of  earth,  45. 

Flying  fish,  308. 

Flying  lemurs,  297. 

Fog,  195,  242. 

Folding,  86. 

Food  plants,  288. 

Foothills,  76. 

Force  of  waves,  182. 

Forests,  submerged,  93. 

Foxes,  white,  292. 

Franz  Josef  glacier,  263,  265. 

Frigid  zones,  true,  217. 

Fringing  reefs,  132. 

Fumaroles,  49. 

Ganges,  delta  of,  79. 
Garden  of  the  Gods,  98. 
Gardens,  98. 
Garonne,  bore  of,  189. 
Geysers,  42. 
Ghats,  121. 
Giacobini's  comet,  12. 
Ginger,  290. 
Giraffe,  297,  298. 
Glacial  grooves,  270. 
Glacial  motion,  262. 

causes  of,  265. 

theory  of,  264. 
Glacial  period,  268. 

of  North  America,  269. 
Glaciers,  261. 

as  river  sources,  271. 

continental,  273. 

distribution  of,  272. 

size  of,  272. 
Globigerina,  178. 
Goats,  292,  296. 
Gobi,  Desert  of,  121. 
Godwin-Au.sten,  mountain,  120. 
Gold  Hill  mines,  temperature  of,  40. 


Gorilla,  297. 

Gradient,  230. 

Graduating  thermometers,  209. 

Graham  Island,  47,  130. 

Grand  Banks,  fogs  of,  195. 

Grand  Canyon,  90,  91. 

Grand  divisions,  71. 

Grand  Geyser,  43. 

Grapes,  324. 

Gravity,  specific,  198. 

Gravity  springs,  141. 

Great  Basin,  102. 

Great  Geyser,  42. 

Great  gray  kangaroo,  301. 

Great  Lakes,  164. 

Great  Plains,  81. 

Great  Salt  Lake,  103,  159,  162. 

Grecian  Peninsula,  116. 

Green  Mountains,  104. 

Greenwich,  24. 

Gregorian  calendar,  29. 

Gregory  XIII,  Pope,  29. 

Grenelle,  temperature  of  well  at,  41. 

Grizzly  bear,  299,  302. 

Grooves,  glacial,  270. 

Ground  swell,  181. 

Ground  waters,  140-144. 

Guiana,  higliland  of,  no. 

Guinea  fowls,  297. 

Gulf  Stream,  193,  194,  213. 

Gulf  weed,  287. 

Gulls,  292. 

Gums,  291. 

Gu.shers,  42. 

Gutta-percha,  309. 

Hail,  201,  258. 

Halo,  278. 

Hammerfest,  climate  of,  213. 

temperature  of,  195. 
Height,  of  the  land,  75. 

of  tides,  188. 

of  waves,  180. 

and  temperature,  213,  216. 
Helium,  200. 


IXDKX 


339 


Hemp,  291,  324. 
Henderson  meteorite,  13. 
Herbivorous  animals,  282. 
Hercules,  constellation,  17. 
High  barometer,  205. 
Highlands,  76. 
High  Sierra,  100. 
High  tides,  183. 
Hills,  76. 

Himalayas,  119,  120. 
Hindu  Kush,  120. 
Hippopotamus,  297. 
Honey  bear,  297. 
Hood,  Mount,  loi. 
Horizon,  171. 

Horizontal  zones  of  vegetation,  284. 
Horns,  86. 

Horse,  292,  296,  301. 
Horse  latitudes,  223. 
Hot  springs,  41,  42. 
Humboldt  current,  197. 
Humboldt  Lake,  103. 
Humidity,  239. 
Humming  birds,  301. 
Hydrosphere,  21,  22,  70. 
Hypothesis,  nebular,  14,  15,  45. 
planetesimal,  14,  16,  202. 

Iberian  Peninsula,  117. 
Ice,  lighter  than  water,  137. 

melting  point  of,  45. 
Icebergs,  273. 
Iceland,  geysers  in,  42. 
Inclination  of  needle,  34. 
India,  flora  of,  309. 

plains  of,  123. 

rainfall  of,  251. 
Indian  corn,  288. 
Indian  Ocean,  174. 

currents  of,  197. 
Indians,  American,  317. 
Indigenous  civilization,  318. 
Industries  of  United  States,  323. 
Inferior  highlands,  95,  117,  120,  123. 
Inland  climate,  211. 


Inland  seas,  160,  161. 
Inorganic  bodies,  280. 
Insular  climate,  211. 
Interior  plains,  76. 
Internal  heat,  40. 
Inundations,  166. 
Iran,  plateau  of,  121. 
Iron  Gate,  116. 
Irrigation,  256,  319,  320. 
Islands,  128-134. 

barrier,  182. 

continental,  128. 

coral,  130-134. 

oceanic,  129. 

volcanic,  130. 
Isobars,  205. 
Isoclinic  lines,  36. 
Isogenic  lines,  36. 
Isothermal  lines,  216. 

and  life,  293. 

map,  214-215. 
Italian  Peninsula,  117. 

Jalap,  291. 
James  River,  105. 
Japan,  earthquakes  in,  64,  65. 
Japan  current,  196. 
Jetties,  148.   - 
Julian  calendar,  29. 
Jungfrau,  115. 
Jupiter,  II. 
year  of,  26. 

Kamerun  ^Mountains,  124. 
Kames,  271,  272. 
Kangaroo,  298,  301. 
Karakoran  Mountains,  120. 
Kashmir  goat,  305. 
Kenia,  Mount,  123. 
Khamsin,  226. 

Khajia  hills,  rainfall  of,  251. 
Khin-Gan  Mountains,  121. 
Kilauea,  46. 

Kilimanjaro,  Mount,  1,23. 
Killarney  Lakes,  163. 


340 


INDEX 


Kirghiz  Steppes,  122. 
Krakatoa,  54. 
Krypton,  200. 
Kuen-Lun,  120. 
Kuro-Shiwo,  196. 

Labor,  distribution  of,  322. 

Labrador,  climate  of,  213. 

Labrador  current,  196. 

Laccolite,  88. 

Lagoon,  132. 

Lahontan,  Lake,  103,  162. 

Lakes,  155-164. 

causes  of,  155,  156. 

desiccated,  161-163. 

distribution  of,  164. 

extinct,  103,  161-163. 

offices  of,  163. 

salt,  158-162. 
Land,  distribution  of,  70-72. 
Land  winds,  253. 
Latent  heat,  137,  138. 
Lateral  moraine,  267. 
Latitude,  23,  24. 
Latitudes,  horse.  223. 
Lava,  49,  50,  54,  55. 
Leap  year,  29. 
Lemurs,  297. 
Lightning,  275. 

kinds  of,  276. 
Lions,  292,  296. 
Lisbon  earthquake,  65. 
Lithosphere,  21,  22,  70. 
Liverpool,  tides  at,  189. 
Livingstone  Mountains,  123. 
Llama,  301,  304,  306. 
Llano  Estacado,  82. 
Llanos,  76,  iii. 
Logwood,  291. 
Loma  Point,  179,  180. 
Longitude,  23,  24. 
Longitudinal  valleys,  89. 
Low  barometer,  205. 
Low  tide,  183. 
Lowlands,  76. 


Lunar  day,  183,  185. 
Lyre  bird,  298. 

"Mackerel  sky,"  244,  245. 
Macrocystis  pyrifera,  287. 
Magdalena  River,  108. 
Magnet,  32. 

Magnetic  declination,  37. 
Magnetic  equator,  34. 
Magnetic  field,  33. 
Magnetic  needle,  ;^;^. 
Magnetic  north  pole,  34. 
Magnetic  parallels,  36. 
Magnetic  poles,  7,7,. 
Magnetic  storms,  38. 
Magnetism,  terrestrial,  32. 
Magpies,  296. 
Mahogany,  291. 
Maladetta,  Mount,  116. 
Malay  race,  317. 
Malay  tiger,  304. 
Mai  de  montagne,  205. 
Man,  races  of,  311,  314. 

range  of,  311. 
Mandioca.     See  Manioc. 
Mango,  309. 
Manioc,  289,  290,  310. 
Manufacturing,  325,  326. 
Maple,  291, 
Maravaca,  no. 
Marine  deposits,  176-178. 
Maritime  climate,  211. 
Marlin,  temperature  of  well  at,  41. 
Mars,  II. 
Marsupials,  298. 

Materials  for  Physical  Geography,  330. 
Matterhorn,  the,  85,  116. 
Mauna  Kea,  48. 
Meanders,  147,  148. 
Medial  moraine,  267. 
Medicinal  plants,  291. 
Mediterranean  Sea,  saltness  of,  172. 
Melting  point,  45. 
Menam  valley,  overflow  of,  79. 
Mercurial  barometer,  203. 


INDKX 


341 


Mercurial  thermometer,  208. 
Mercury  (quicksilver),  198,  203,  208. 
Mercurj'  (planet),  11. 

year  of,  26. 
Mer  de  Glace,  262. 
Meridians,  23. 
Mesa,  84. 

Meteoric  swarms,  12,  14. 
Meteorite,  Henderson,  13. 
Middav  lines,  23. 
Millet,' 288. 
Mineralization,  42. 
Miner\a  Terrace,  42. 
Mines,  temperature  of,  40. 
Mining,  326. 
Mirage,  279. 
Mississippi  basin,  107. 
Mississippi  River,   amount    of    water 
in,   167. 

banks  of,  150. 

delta  of,  79,  149,  150. 

erosion  by,  146. 

floods  in,  163,  166. 

jetties  of,  148. 

meanders  of,  147. 
Mistral,  226. 
Mitchell,  Mount,  105. 
Mocking  bird,  299. 
Mock  suns,  278. 
Moisture  of  the  air,  239. 
Moles,  296. 
Mongolian  race,  315. 
Monkeys,  301. 
/l^Ionsoons,  198,  224. 

effect  of,  225. 

minor,  226. 
Mont  Blanc,  116,  261. 

boiling  point  at,  204. 
Mont  Cervin,  85. 
Mont  Pelee,  54. 
Monte  Rosa,  116. 
Monument  Park   99. 
Moon,  eclipse  of  the,  19. 
Moondogs,  278. 
Moons,  II. 


Moraines,  267. 
Motions  of  the  earth,  23. 
Mot-mots,  301. 
Mountain  chain,  86. 
Mountain  crest,  86. 
Mountain  flanks,  86. 
Mountain  knots,  108. 
Mountain  peaks,  86. 
Mountain  range,  86. 
Mountain  sickness,  205. 
Mountain  system,  86. 
Mountains,  76,  85,  95-127. 

formation  of,  86. 

regulators  of  rainfall,  251. 

block,  88,  102. 
Movements,  earth,  75. 
Mozambique  current,  197. 
Musk-ox,  292. 

Narcotics,  290. 

Natural  magnet,  32. 

Neap  tides,  187. 

Nebula,  15. 

Nebular  hypothesis,  15,  45. 

Needle,  magnetic,  ^^^. 

declination  of  the,  36. 

dip  of  the,  34. 
Negro  race,  316. 
Neptune,  11. 

year  of,  26. 
Neutral  line  (magnetic),  ;^^. 
New  Caledonia  reefs,  132. 
New  Madrid  earthquake,  65. 
New  River,  105. 
New  Style,  29. 
New  Zealand,  springs  in,  42. 
Newton,  25. 

Niagara  Falls,  145,  152-156. 
Nightingales,  296. 
Nile  River,  80,  169,  170. 

delta  of,  149. 
Nile  valley,  overflow  of,  79,  80. 
Nimbus,  246. 
Nitrogen,  200. 
North  .America,  drainage  of,  i()~ 


342 


INDEX 


North  America,  flora  of,  310. 

glacial  period,  269. 

rainfall  of,  252. 

relief  of,  95-107. 
North  Cape,  117,  118. 
North  Carolina,  coastal  map,  129. 
North  Pacific  current,  196. 
North  pole,  24. 
North  star,  24. 
Northern  Hemisphere,  71. 
"Northers,"  226. 
Norway,  climate  of,  213. 
Nucleus,  earth's,  22. 
Nutmeg,  290. 

Oak,  291. 

Oases,  126. 

Oblate  spheroid,  earth  an,  20. 

Ocean  currents,  190,  191. 

affect  climate,  212. 
Oceanic  circulation,  197. 
Oceanic  Islands,  129. 
Oceans,  1 71-178.      See  Sea. 
Oil  palm,  309. 
Old  Faithful  Geyser,  44. 
Olives,  309,  325. 
Olympus,  Mount,  117. 
Ooze,  178. 
Opium,  290. 
Opossums,  298,  299. 
Oranges,  325. 
Orang-outang,  297,  299. 
Orbits,  10. 
Orchard  fruits,  324. 
Oregon,  climate  of,  213. 
Organic  bodies,  280. 
Orinoco  River,  i  ro,  iii. 

delta,  149. 
Orizaba,  climate  of,  216. 
Orkney  Isles,  temperature  of,  195. 
Ostend,  184. 
Ostrich,  305. 
Ox   292,  301.  , 

Oxbow,  147. 
Oxygen,  200. 


Oysters,  308. 

Pacific  current,  196. 
Pacific  Highland,  95,  107. 
Pacific  Ocean,  174-178. 
Pamir,  119. 
Pampas,  76,  in. 
Pamperos,  226. 
Papandayang,  58. 
Parallels,  23. 

magnetic,  36. 
Paraselenae,  278. 
Parhelia,  278. 
Parime  Mountains,  no. 
Parks,  98,  99. 
Passes,  91. 
Passion  flower,  310. 
Peacock,  298. 
Peaks,  mountain,  86. 
Pear,  309. 
Pelee,  Mont,  54. 
Pe-Ling  Mountains,  120. 
Pepper,  290. 
Periodical  rains,  254. 
Periodical  winds,  224. 
Persimmon,  310. 
Peruvian  current,  197. 
Pheasant,  Argus,  298. 
Pheasants,  292,  296. 
Phosphorescence,  in  sea,  173. 
Physical  features,  75. 
Physical     geography,    influenced     by 
man,  319. 

manner  of  studying,  329. 

related  to  other  sciences,  328. 

scope  of,  328. 
Piedmont  belt,  100. . 
Pikes  Peak,  97. 
Pimento,  290. 
Pines,  291. 
Plain,  delta,  79. 
Plains,  76. 
Planetesimal      hypothesis,      14,      16, 

202. 
Planetesimals,  16. 


INDEX 


343 


Planetoids,  lo,  12. 
Planets,  11. 

relative  sizes  of,  16,  17,  21. 
Plants,  distribution  of,  282. 

higher,  280. 

medicinal,  291. 

used  for  clothing,  291. 
Plata  River,  no,  in. 

no  delta,  150. 
Plateaus,  76,  82-84. 

of  Africa,  123-125. 

of  Asia,  119,  121. 

of  North  .America,  97,  100-104. 

of  South  America,  109,  no. 
Playas,  102. 
Po  River,  150,  166. 
Point  Loma,  179,  180. 
Pointers,  24. 
Poisonous  serpents,  292. 
Polar  currents,  192,  196. 
Polar  winds,  223. 
Polar  zones  of  vegetation,  284. 
Poles,  24. 

magnetic,  ;^;^. 
Polyps,  130,  131,  197. 
Pope  Gregory  XIII,  29. 
Position,  23. 
Potato,  289,  310. 
Potomac  River,  105. 
Pouched  rat,  299. 
Prairie  dogs,  299. 
Prairies,  76,  107. 
Precipitation,  240. 
Prehensile -tailed  monkey,  301. 
Prevailing  winds  and  climate,  212. 
Problem  of  Eratosthenes,  24. 
Pumice,  50. 
Puna,  226. 
Pyramid  Lake,  103. 
Pyrenees,  116. 

Quartz,  41. 

Quicksilver,  weight  of,  198. 

Quinine,  291. 

Quito,  boiling  point  at,  204. 


3^2,  313,  314. 


Raccoons,  299. 
Race,  tide,  188. 
Races  of  mankind, 
Radiolaria,  178. 
Rain,  201. 

cause  of,  249. 

classitication  of,  253. 

constant,  254. 

deficient,  255. 

distribution  of,  248,  249. 

excessive,  255. 

periodical,  254. 

regulators  of,  251. 
Rainbows,  279. 
Rainless  regions,  257. 
Rainy  season,  255. 
Range,  geographical,  282. 

mountain,  86. 

of  draught  animals,  301. 
Rapids,  150,  153. 
Rattlesnake,  299. 
Reclaimed  land,  320. 
Red  clay,  178. 
Red  Sea,  saltness  of,  172. 
Reefs,  coral,  131,  132,  197. 
Reflection  of  light,  278. 
Refraction  of  light,  278. 
Regelation,  265. 
Regions,  zoological,  292. 

of  life,  296. 
Reindeer,  292,  302. 
Relief  of  the  land,  75. 

causes  of,  93. 

continental,  95. 

effects  of,  94. 

forms  of,  76. 

of  Africa,  123-126. 

of  Asia,  1 19-123. 

of  AustraHa,  126,  127. 

of  Europe,  11 2-1 19. 

of  North  .\mcrica,  95-107. 

of  South  America,  107- in. 
Reservoir,  underground,  142. 
Return  currents,  192. 
Revolution  of  the  earth,  23,  25. 


344 


INDEX 


Rheas,  301,  305.       • 

Rhinoceroses,  292. 

Rhone  River,  matter  transported  by, 

146. 
Rice,  79,  288,  289,  324. 
River  basin,  165. 
River  plains,  76. 
River  system,  144. 
Rivers,  165-170. 

sources  of,  144,  271. 

tides  of,  189. 
Robins,  299. 
Rocky  Mountains,  97. 
Rosa,  Monte,  116. 
Rosewood,  291. 
Rotation  of  the  earth,  23,  25. 
Ruwenzori  Mountains,  123. 
Rye,  288. 

Sables,  292. 
Sahara,  125. 

cHmate  of,  212. 
Saint  Elmo's  Fire,  278. 
Saint     Gothard    tunnel,    temperature 

of,  40. 
Saint  Michael,  springs  at,  41. 
Salt,  in  sea,  171,  172. 
Sand,  volcanic,  50,  53. 
Sand  dune,  125,  227. 
Sandalwood,  291. 
San  Francisco  earthquake,  63,  66,  68, 

69. 
Santorini,  130. 
Sao  Francisco  River,  no. 
Sargasso  Seas,  199. 
Sarsaparilla,  291,  310. 
SateUites,  11. 
Saturation,  point  of,  239. 
Saturn,  11. 

and  his  rings,  15. 
Scales,  thermometer,  209. 
Scandinavian  Mountains,  117. 
Sea,  1 71-178. 

bottom  of,  175-178. 

color  of,  172. 


Sea,  currents  of  the,  192. 

depth  of,  174,  175. 

extent  of,  171. 

phosphorescence  of,  173. 

saltness  of,  171,  172. 

temperature  of,  174. 
Sea  waves,  earthquake,  63,  64. 
Sea  winds,  253. 
Seal,  292,  308. 
Seasonal    variation    in    temperature, 

207. 
Seasons,  change  of,  29. 
Secretary  bird,  297. 
Secular  variations,  38. 
Sequoia  gigantea,  310. 
Serpents,  poisonous,  292. 
Sharks,  308. 
Sheep,  292,  296. 
Sheet  lightning,  276. 
Shooting  stars,  14. 
Shore  lines,  delta,  79. 
Shoshone  Falls,  155. 
Siam,  rice  crop  of,  79. 
Siberian  Plain,  122. 
Sidereal  day,  28. 
Sierra,  86. 
Sierra,  High,  100. 
Sierra  Nevada,  100. 
Silica  in  geysers,  43. 

in  springs,  41. 
Silicious  ooze,  178. 
Silt,  146. 
Silvas,  76,  no. 
Silver-tip  grizzly  bear,  302. 
Simoom,  235. 
Sinter,  41. 
Sirocco,  226. 
Skaptar  Jokul,  54. 
Skunks,  299. 
Sloth,  301,  305. 
Snake  River,  loi,  155. 
Snow,  201,  258. 

uses  of,  259. 
Snow  line,  258. 
Snow  Mountains,  123. 


i 


IN'DKX 


345 


S  )ft  rocks,  erosion  of,  84. 
Solar  day,  2S. 
Solar  system,  10,  11. 

origin  of,  14. 
Solstice,  winter,  27. 
Solstices,  26. 
South  America,  drainage  of,  167,  i6vS. 

tlora  of,  310. 

rainfall  of.  251. 

relief  of,  107  11 1. 
South  magnetic  ix)le,  34. 
South  pole,  24. 
Southern  Hemisphere,  71. 
Spanish  peninsula,  117. 
Specific  gravity,  198. 
Sperm  whale,  308. 
Spheroid,  oblate,  20. 
Spices,  290. 
Spits,  182. 
Sponges,  308. 

Spot  period  of  the  sun,  39. 
Spring  tides,  183,  185. 
Springs,  140,  141. 

hot,  41. 

algae  in,  42. 
Standard  time,  28. 
Stars,  fixed,  11. 

shooting,  14. 
Steppes,  76,  122. 
Storm  cards,  231. 
Storm  laws,  value  of,  233. 
Storms,  229.    • 

areas  of,  233. 

cause  of,  229. 

distribution  of,  235. 

laws  of,  231. 
Storms,  magnetic,  38. 
Strata,  dip  of,  77,  78. 
Stratus  cloud,  245. 
Stromboli,  50,  52. 
Submerged  forests,  93. 
Subsidence  of  land,  92. 
Sugar,  324. 
Sugar  cane,  290,  293. 
Sulaiman  Mountains,  121. 


Sun,  14. 

spot  period  of,  39. 
Sundogs,  278. 
Superior,  Lake,  164. 
SujDerior  highland,  95. 
Sus(|uehanna  River,  105. 
Sweet  ]x)tato,  309. 
Sycamore  tig,  309. 
System,  mountain,  86. 

Table-lands,  76,  82. 
Tahiti,  134. 
Tailor  birds,  298. 
Tea,  290. 
Teak,  291,  309. 
Telegraphic  plateau,  176. 
Temperate  zone,  of  animal  life,  292. 
Temperate  zones,  of  vegetation,  284. 

true,  217. 
Temperature,  atmospheric,  206. 

measuring,  208. 

seasonal,  207. 

of  zones  of,  217. 

of  artesian  wells,  41. 

of  Calumet-Hecla  mine,  40. 

of  Comstock  lode,  40. 

of  Gold  Hill  mines,  40. 

of  Gulf  Stream,  194. 

of  Hammerfest,  195. 

of  Orkney  Isles,  195. 

of  Saint  Gothard  tunnel,  40. 

of  Werchojansk,  212. 

and  climate,  210. 

and  height,  213,  216. 
Terminal  moraine,  267. 
Terraces,  92. 

Terrestrial  magnetism,  32. 
Thermal  springs,  41. 
Thermometer,  203,  208. 
Thian  Shan,  120. 
Thrushes,  299. 
Thunder,  276. 
Tibet,  plateau  of,  82,  119. 
Tidal  wave,  movement  of,  187. 
Tides,  183. 


346 


INDEX 


Tides,  height  of,  i88. 

neap,  187. 

spring,  185. 

of  rivers,  i8q. 
Tide-water  country,  324. 
Tigers,  292,  297,  304. 
Till,  269. 

Time,  standard,  28. 
Titicaca,  Lake,  108,  164. 
Tobacco,  290. 
Todies,  301. 
Tomboro,  58. 
Tornado,  234. 
Tornadoes,  233. 
Torricelli's  experiment,  202. 
Torrid  Zone,  true,  217. 
Toucans,  301. 
Trade  winds,  221. 
Transportation,  146. 
Transporting  agents,  182. 
Transverse  valleys,  89. 
Tree  kangaroo,  298. 
Trees,  useful,  291. 
Trogon,  298. 
Tropic  of  Cancer,  30. 
Tropic  of  Capricorn,  31. 
Trough  of  wave,  179. 
Tsien-tang,  bore  of,  189,  192. 
Tufa,  162. 
Turkestan,  121. 
Turkey,  292. 
Tuscarora  deep,  175. 

Universe,  earth  and  the,  17. 
Upward  fold,  87. 
Uranus,  11. 
Ural  Mountains,  117. 

Valdai  Hills,  it8. 
Valleys,  89. 
Vampire  bat,  301. 
Vapor,  water,  201. 
Variable  rains,  255 

winds,  221. 
Variations,  diurnal,  38. 


Variations  in  declination,  38. 

in  pressure,  204. 

secular,  38. 
Vegetables  modified  by  climate,  283. 
Vegetation,  zones  of,  283. 
Velocity,  of  clouds,  247. 

of  wave  movements,  181. 
Venus,  II. 

Vernal  equinox,  26,  207. 
Vertical  zones  of  vegetation,  286. 
Vesuvius,  48,  50-53,  54. 
Victoria  Falls,  155. 
Victoria  Lake,  164. 
Victoria  Regia,  281,  310. 
Vicuna,  304. 

Vindhya  Mountains,  121. 
Volcanic  cones,  46-48. 
Volcanic  islands,  129,  130. 
Volcanoes,  43,  46-59. 

causes  of  action,  58-59. 

cla.ssified,  50. 

distribution  of,  55-58. 

eruptions,  51-55,  58. 

products,  48-50. 
Volga,  delta,  149. 
Vulcanic  plateaus,  82. 
VulcanLsm,  86. 

Walker  Lake,  103. 
Walnut,  291. 
Walrus,  292. 

Washington,  Mount,  105. 
Water,  absorption  of  heat,  137. 

circulation  of,  139. 

composition  of,  136. 

evaporation    and    condensation   of, 

138,  139- 

expansion  of,  136. 

forms  of,  136. 

properties  of,  136-139. 

solvent  power  of,  139. 
Waterfalls,  151- 15  7. 
Water  gap,  91. 
Waters  of  the  land,  140-164. 
Watershed,  165. 


INDEX 


347 


rocky    headland, 


Waterspxnit,  235. 
Wave,  tidal,  187. 
Wave    action,   on 
182. 

on  submerged  rocks,  181. 
Wave  movements,  velocity  of,  181. 
Waves,  179. 

force  of,  182. 

height  of,  180. 
Weather  and  climate,  210. 
Weather  forecasts,  237. 
Weather  map,  236. 

description  of,  238. 
Weaver  birds,  297. 
Welh,  temperature  of  artesian,  41. 
Werchojansk,  climate  of,  212. 
\\'est  Indian  boa,  309. 
Westerlies,  prevailing,  221. 
Whale,  292,  308. 

right,  308. 
Wheat,  288,  324. 
Whirlpool,  189. 
Whirlwind,  233. 
"Whirlwind,  dust,"  234. 
White  bear,  292. 
White  foxes,  292. 
White  Mountains,  104. 
Whitsunday  Island,  133. 
Wicklow,  tides  at,  189. 
"Wind  roads,"  234. 


Winds,  218. 

alTect  climate,  212. 

cause  of,  218. 

constant,  221. 

periodical,  224. 

|X)lar,  223. 

surface  effects  of,  227. 

trade,  221. 

variable,  221,  255. 
Winnenucca  Lake,  103. 
Wolf,  292,  296. 
Wombat,  298. 
Wrens,  299. 
Wyoming,  springs  in,  42. 

Yak,  305. 

Yellowstone,  Falls  of,  155. 

Yellowstone   National   Park,   springs 

and  geysers  in,  42,  44. 
Yoseraite  Falls,  155,  157. 

Zagros  Mountains,  121. 
Zambezi  River,  falls  on,  155. 
Zenith,  24. 

Zigzag  lightning,  276. 
Zones,  of  animal  life,  292. 

of  temperature,  217. 

of  vegetation,  283. 
Zoological  regions,  292,  294,  295. 


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